[Seek]

10 years later, completely different topend, this is still happening: https://www.eectuning.org/forums/viewtopic.php?t=15381

Cold to hot datalog taken today. http://masejoer.com/Projects/Thunderbir ... -47-36.zip

I've been battling this for apparently a decade now. At a loss of where to look now. Car has not had many miles since my old thread.

Now that I'm tackling it again, does anything in the above datalog look off (other than the wideband map needing to be tweaked)?

This datalog was from a EEC reset (battery disconnected for 30 minutes), and full warmup.



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My powertrain specifications:

Stock-type 306 rebuild from 15 years ago, 20k miles on the rotating assembly:
TRW-L2305F30 pistons
SLP-E-251K030 rings
SCA-35090P i-beams
Stock 1989 Mustang camshaft
Stock pan, pump, crank machines and balanced with the rotating assembly
Powerbond 50oz SFI balancer
Timing setup dot to dot, and seems correct for TDC marks on balancer for each cylinder when I tried leakdown tests

Rest of engine (newer than shortblock):
TW 170cc heads cut down to 54cc chambers (lots of clearance with 1.7 rockers, clayed)
Comp-cams high energy hydraulic roller lifters set to 0.025 preload
Whatever pushrod length was needed when the heads were initially installed
GT40 tubular intake with lower porrted by tmoss
19lb stock injectors, and 30lb FMS injectors
Stock MAF, and PMAS 75mm "24lb" MAF
Accufab 70mm throttle body
FMS stainless "gt40p compatible" shorty headers with 1-5/8" primaries
Autolite 3924 plugs gaps tested at .040 and.050
MSD spark wires, <100 miles
Stock distributor/TFI, and Richporter FD04 replacement
Standard "195" thermostat
New Motorcraft TPS
New Motorcraft air charge and engine temp sensors
Various gaskets, 9.8:1 static compression ratio.
EGR and IAC still installed
Currently have fresh 92 octane ethanol-free fuel

Drivetrain:
4R70w transmission/stock VB/clutches from 2003 3.8L
Larger capacity trains oil pan with cooling fins
PI Stallion 3000 stall converter
Stock driveshaft
8.8" rear differential with 3.55 gears, 26.6" wheel diameter

Other:
1989 A9P ECU with new capacitors
Quarterhorse tuning board
New Motorcraft fuel regulator
2.5" exhaust, catalytic converters intact (few hundred miles)
Larger, soldered engine grounds with contact areas using NO-OX grease
Dual Innovate LC-2 wideband sensors mounted horizontally near bottom of exhaust down-pipes
DataQ datalogger for widebands
Young narrowband o2s that sweep well
1/0 gauge alternator power wire, 4awg timing cover to battery ground, 7awg dual braided head to firewall grounds, crimped and soldered terminals

Much of the above hasn't seen more than around 100 miles in over 5 years. A week ago it was driven to a glass shop, and likely doubled the mileage it has seen since being driven to a new house years ago.

[Seek]

What I've done/re-tested lately:

- Smoke machine intake test, no leaks with oil filler cap taped down
- Distributor swapped out with a new unit, new TFI, as a test. No change. Caps/rotors still both look new.
- New BAP, TPS, air charge, engine temp sensors
- New IAC
- IAC block off
- Rocker arms checked to ensure preload
- EGR valve tested
- Cleaning of TFI plug
- Cleaned and increased contact tension of the salt and pepper connectors at engine harness
- New battery
- Shaken/wiggling harness connections when running to look for change in idle quality (none)
- 30lb EV6 Injectors flow tested - good.
- Reinstalled some original refurb/flow tested 19lb EV1 injectors to test stock tune.
- MAF seems to sweep fine, but reinstalled stock 1989 MAF to test stock tune.
- Leakdown test shows 8-10% across all cylinders. No sound from intake or exhaust - crankcase only.
- 165-170psi compression test across all cylinders
- plugged off vacuum lines an pcv, no vacuum at oil filler tube (lower intake gaskets should be good). Slight vacuum at oil filler tube with pcv re-attached.
- no exhaust smoke
- no coolant or oil issues
- stock tune (minus increasing CID to 306, and disabling thermactor) with stock injectors and MAF
- new engine bay grounds with conductive grease
- cleaned and re-mounted eec-iv computer grounds
- spark timing at 10 degrees base. According to tuning software, issue still exists at all timing so not a timing advance issue
- timing markings should be correct on balancer - markings seem to match TDC of various cylinders perfectly (for leakdown test)
- no engine running codes. Cylinder balance test comes back as passing
- engine is idling fine at 650-750rpms, around the 672 being commanded. Should be more steady.
- 16in/Hg vacuum at warm idle with all vacuum accessories attached, 1300rpm and above get 20in/Hg
- Coolant temperature is a steady 206-208F at temperature sensor when idling or driving, 160F intake runner temperature at idle in garage
- I've tried completely isolating plug wires into air as a test, but no change
- Spark plugs all look great
- Correct firing order
- Timing light on each wire doesn't appear to have any missing ignitions. I hoped to find one with occasional missing flashes...
- Replaced capacitors in A9P
- Binary Editor datalogs generally look good - the stumble isn't timing swinging around.
- Idle doesn't improve if I richen up the AFR. Leaner than stoich just starts to stumble, as expected.
- Fuel pressure 40psi without vacuum, 33psi at idle with vacuum.
- New alternator due to failing bearings. New alternator's AC ripple is 29mA.
- EGR block off
- New coil
- Unplug Quarterhorse completely and run stock tune only with stock MAF/injectors
- Cleaned EEC-IV connector and J3 port

Things that I still want to check:
- Replace salt/pepper engine harness connectors with 12-pin deutsch connectors
- New coil again? Years ago I tried a new aftermarket coil, but it would breakup badly at 2500+ rpms. I went back to my old coil.
- Exhaust smoke machine test
- Try a completely different A9P?

Other plans:
- EDIS-8 to ditch TFI altogether. Just need a crank pulley to take to machine shop with trigger wheel for welding/balancing
- Install my Lightning MAF, for potential better metering than the aftermarket unit, unrelated to stock air/fuel parts and tune
- Maybe removing the exhaust to see if my issue has nothing to do with the motor, but ignition in the cats sending waves back up to the motor, messing with cylinder activity?
- New seal on oil filler lid since I get a slight leak under pressure from the smoke machine

[Seek]

Engine currently has 19lb EV1 injectors that I rebuilt a few weeks ago, stock '89 Mustang MAF, QH with stock A9P/GUF1 tune other than CID increased to 306, EGR disabled (blockoff plate is still installed), smog disabled.

I've gone as back to "stock" as I can while trying to troubleshoot this. So far none of the stock metering and fuel parts have improved the situation.

[cgrey8]

Is it a rough idle or a hunting idle?

[Seek]

"Rough" as in not smooth like a v8 (with a factory cam) should be. No hunting. Drives great otherwise.

I've been trying to diagnose it off and on for the last decade as a misfire, but so far haven't found anything to actually solve it. When shortblock was built, the entire rotating assembly, balancer, and flex plate was dropped off at the machine shop, and it doesn't seem to run like a balance issue, but more a misfire.

Balancer markings look to be dead on when getting to TDC for the leakdown tests.

[cgrey8]

Is there any chance you advanced or retarded the cam when installing the timing kit?

I could see that affecting low RPM/Load conditions like idle. Most times you might would advance a stock cam 2-4 degrees. But if it were to get retarded, this would delay closing the exhaust valves thus sucking exhaust back into the cylinder at low RPMs. I could see how that would cause combustion instability, but would quickly disappear as the RPM/Loads got higher.

If it's acting like it is misfiring at idle, it's likely doing this on more than one cylinder. Based on my (very limited) experience, when I had fuel or spark problems, they were undetectable at idle and only noticeable under load...because both the original 302 was stock and the 331 I have now is very mild thus both idled so smooth that being down a cylinder was hard to detect by ear or feel until the throttle was blipped. Point is, if it is running rough, I would expect it's most or all cylinders that are affected and a cam being out of time would certainly affect all cylinders.

[Seek]

Timing chain was simply installed "dot to dot", some 11-12 years ago when the shortblock was done (mostly by my dad - I knew next to nothing about motors back then). I thought about potential cam timing issues, but not sure how to verify without teardown. It has a stock replacement chain with the stock crank and cam - dot to dot shouldn't be off anymore than other cars from the factory.

If I knew it was the timing and was worth investigating via R&R, I'd have the thing torn down and back together this weekend. I've already done just about everything else. Wish I would have looked into this years back when I replaced the timing cover gasket.

You still may be onto something through. Having not been measured, the cam timing could still be off, stock or not. It's some $200 to pick up all of the replacement gaskets, new timing set ,and degreeing kit.


I remember back around the year 2000 with this car's stock Standard-Output motor, once I didn't plug a spark wire in, or it was loose. I couldn't tell until getting onto the highway and being a bit down on power. The thing ran smooth. I don't get that with this motor, but it's also completely different. Only the block and crank were machined/reused, and I guess the wiring harness. Everything else has been changed many times over.

[FoMoCo17]

Wow ... and I thought I was the only one with this problem! Everything you’ve done, I’ve also done incl soldering 10 pin connector wires together. Mines got a Kenne Bell on it too which could be part of the problem. But, I have a lot of idle rpm variance and a lot of spark control jumping around a lot also. I’ve checked n checked for vacuum leaks etc etc.. seems at idle I do have some sort of misfire that I feel n hear in exhaust under my seat ... just cannot figure this problem out. I need to get back on idle tuning but did the basics which helped some. It seems to perform fine and runs smoother in drive. I did set one of the “neutral” tables you mentioned to be the same as the “drive” table and that helped a bit along with putting a honeycomb before the maf. And it should just idle better! Some how I think this misfire/crossfire is causing it on drivers bank but am not finding it ... searching for a decade like you also after a rebuild to a 306 w forged bottom end and stock top end exc the Kenne Bell ... though everything was ported alone w Covra 1.7 roller rockers. Initially adding fuel helped bec it was lean ... but it doesn’t solve it! I have to go back and explore the idle in BE along w this crossfire/misfire I tend to feel/hear. Everything always seems to checkout out okay and is functioning ... so it is baffling!!! I’ve checked lifter preload 3 times along w intake gaskets two or three times. And it even seems to do it w all vacuum sources disconnected. I pull 16-17 inches of vacuum in neutral and 14-15 in drive. And at 800- 1000 I’m pulling like 18-20.

If you find the cause or anything helpful please post it .. I will do the same though I only research it fr time to time but def wanna solve it!

[Seek]

Sorry to hear that you have what sounds like a near identical issue. We must get this solved!

It still "drives" fine, but there's more to a car than just WOT on the strip, or around town. The entire package should perform well, even if it's something as "small" as idle quality.

I was very close to just tearing it all out and going Coyote swap, but would prefer not for various reasons. $10k swap seems like a drop in the bucket compared to all I've "gone through" on this car so far. I spend the time and money because I MUST KNOW WHY. But eh, it's a "labor of love", and pain. Becoming one of the more difficult relationships.

While it's still "throwing parts at the problem", I may very well pull the timing set (and install new) this weekend and degree the cam. See where it's at, and advance it a bit while in there. We spend more time at the lower load on the street, so advancing it shouldn't do anything negative for street drive-ability.

[cgrey8]

Spark jumping around? I know the stock tunes did this to attempt to control hunting. But I found with my setup that hunting was actually caused by over-shooting spark at idle. So I modified my Idle Spark functions to limit how much they could jump around at idle and now my spark commanded values at idle are far more stable.

I don't know that this will help any with either of your problems, but rough idle is, IMO, an indication that each cylinder fire is somehow fundamentally different than the one before causing the roughness. If spark is jumping around, that could contribute to why each are different.

Another thing that could cause this that is not easily fixed is if there's a gross difference in chamber volume or shape. This is quite possible with stock heads or heads where someone has done porting work to the heads. If the chambers were modified and done so in an inconsistent way so as to cause different volumes, this would mean each cylinder is firing different than the other because each cylinder chamber is enough different. However it's not likely to be an issue on aftermarket heads.

A similar problem can happen if the machine shop was not good at keeping the decks perfectly flat such that the amount each cylinder is "in the hole" or popping up at TDC is different. I was particularly interested in making sure my machinist got this right and he didn't the 1st AND 2nd time!!!! It took 3 tries and another block later (supplied by him) for him to get it right. But now my pistons are all within +/-.001 of each other, targeting .005" popping out of the holes. My guess is most people just trust the machinist and don't check this. My personal experience has told me that's a bad idea!

[EDS50]

How does the car idle with the vac line off the fpr? Have you tried a different fp gauge to confirm your fuel pressure setting? How did you set the lifter preload. I know you mentioned 0.025. With your heads the rockers should be tightened at operating temp 1/2 to 3/4 turn past zero lash before tightening the locks if they are adjustable rockers. Also, have you ever had the valve spring seat pressure tested?

[FoMoCo17]

Thanks Cgrey and ED550,

I’m writing this trying to remember each of your points. Anyway, for my case, I’ve done mild porting to clean up around the bowls n seat along w some gasket matching .. nothing major. I did not measure all cylinders at tdc in their bores unfortunately. I did degree cam against Ford specs for my cam(stock) and advanced it 2 degrees based on chain stretch and it being off by 1 degree ... nothing major. I like the idea of controlling how far the spark can actually jump around ... what table or scalar do I adjust for this for an A9P? By the way, my computer was also sent out and repaired incl new capacitors etc.. Possibly the spark is jumping around from the previous adjustment by the computer. As stated previously, I have not gotten into to much depth w adjusting my idle yet and def need to address this again at some point. I have not pulled the vacuum line off the regulator, wouldn’t that just riches the mixture? I’ve got it pretty much at 14.10 now for E10 gasoline. Also, im not sure what your meaning by pressure checking the spring seat .. can you expand on that? Thanks as always ...

Btw... I have cyl’s 1&3 and 5&6 separated in my plug wire harnesses, is there anything else I can do to prevent any type of cross firing if it is occurring ... just put new Bosch wires on it after removing my MSD wires thinking maybe they were the culprit. The misfire I’m hearing in my exhaust during idle and other times just doesn’t seem right to me. I also tried a set of Accel injectors and had my original injectors flowed n balanced by Mark Sanchez at Advanced Engineering and threw them back in (though he did find one that output was low and he replaced it out of his kind generosity) ... just cannot figure out why I seem to also be getting these misfires in exhaust coupled w bad idle quality. I’m also running a MSD distributor but have changed it out w a Ford distributor many times w no difference. Thanks for your help and ideas as always. I’ve solved so many problems on cars over the years, but this one def has me stumped also!

[Seek]

How does the car idle with the vac line off the fpr? Have you tried a different fp gauge to confirm your fuel pressure setting? How did you set the lifter preload. I know you mentioned 0.025. With your heads the rockers should be tightened at operating temp 1/2 to 3/4 turn past zero lash before tightening the locks if they are adjustable rockers. Also, have you ever had the valve spring seat pressure tested?

I'll have to test the vac line thing again - don't recall its details right now, but I will document it in the above post when I test this. I just got this replacement OTC FP gauge weeks ago as I couldn't find my other two. I do have some pressure transducers somewhere that I could bolt on, but not sure where they are at the moment. Haven't used them in years.

Last time I adjusted the lifter preload years ago, I went just past 1/4 turn to make sure the valves were closing (low preload). Didn't help of course, and do want to add more to quiet the valvetrain a little. On the old gt40p heads, I'd shim those pedestals many times to mess with preload, but it never changed how the car ran. I have a photo of needing a 6.665 inch pushrod length (http://masejoer.com/Images/Thunderbird/ ... hrod_4.jpg, I believe i used 6.70" pushrods, purchased Feb 2013. These TW heads must have been installed March 2013, but it didn't change how my engine idled. I think I was hoping it would - the gt40p heads showed this on one cylinder:http://masejoer.com/Images/Thunderbird/ ... Orange.jpg

The shop gave me closed valve seat pressure on the receipt - 130lb. Nothing there about open pressure. Not that this means much, since the idle issue also existed on factory-stock gt40p heads (with only lapped-in valves).

Saw among the photos that it has Trickflow's 1.7 stud rockers: http://masejoer.com/Images/Thunderbird/ ... kerOil.jpg

[FoMoCo17]

Also, w fuel gauge on shrader valve, I’m measuring 39 w vacuum disconnected and like 33-34 w it connected. My valves are not adjustable on my E7 heads but I used shins and after finding zero lash shims were used to preload lifters anywhere between 1/2-1 turn of the bolt ... one head came in between 1/2-5/8 and the other head tended to come in between 3/4-1 (tried it w a lessor shim but was only getting just over a 1/4 turn of preload and was more noisy).

[Seek]

Also, w fuel gauge on shrader valve, I’m measuring 39 w vacuum disconnected and like 33-34 w it connected. My valves are not adjustable on my E7 heads but I used shins and after finding zero lash shims were used to preload lifters anywhere between 1/2-1 turn of the bolt ... one head came in between 1/2-5/8 and the other head tended to come in between 3/4-1 (tried it w a lessor shim but was only getting just over a 1/4 turn of preload and was more noisy).

You sound like me. So much deja vu.

[FoMoCo17]

Yeah I’m using 130 on closed valve spring also due to the supercharger ... my machinist thought it be a good idea w the supercharger to bump up the closed/open spring pressure a bit.

[FoMoCo17]

Yeah when I saw your post I was amazed! You actually documented everything virtually I had also done! I was quite amazed bec you were thinking hard just like I have been and it’s been going on for years! Lol. Then I knew I wasn’t insane! Lol

Do you still have your thermactor system connected?

[Seek]

Yeah when I saw your post I was amazed! You actually documented everything virtually I had also done! I was quite amazed bec you were thinking hard just like I have been and it’s been going on for years! Lol. Then I knew I wasn’t insane! Lol

Do you still have your thermactor system connected?

Thermactor has been gone ever since it seized up on me on the highway some 13-14 years ago with the original SO motor. Bypassed with shorter belt, later removed, and car still passed emissions without issue.

Someone today suggested I install a carb and see if the car idles well without all the electronics. Would be an interesting idle test to perform. I just need an intake and can borrow everything else from a friend.

[EDS50]

My thoughts on the cylinder head valve spring seat pressure likes to be in the 300 range with aftermarket heads. Sounds like your measurement of 150 is low even with e7 heads and stock cam but ill look into those specs further. Your rocker adjustment sounds good for your pedestal mount rockers. Pushrod length sounds correct. We might be getting lost with all the years of info and should concentrate on what is current. Fuel pressure of 33-34 may be too low with vacuum line on. Your combo may want more fuel pressure. Try taking the vac line off regulator and plugging it with a screw and drive the car with static pressure at 40 and see how the car and idle responds. Usually the tiny aftermarket screw in gauges arent very accurate for reading fuel pressure and make sure the schrader valve core is removed from the service port on the fuel rail if that is your source for checking fuel pressure. Your maf sensor is also a key component in dialing in a smooth idle. Forget about going carb, you will not be doing yourself any favors there. The cam being installed straight up or dot to dot vs advanced 2 degrees depends on if the cam has any advance built into it but normally should not result in rough idle. What is important is what your vacuum reading is at idle as that will be a key indicator to many things. You should have no less than 10 in. hg. at idle during normal if not all operating temps. I would recommend to avoid getting lost in translation and detail of years of different parts and settings for us to start from scratch with your current combination and tune and focus on that so we can try to tackle this rough idle issue. If your signature line is current and accurate, that is an excellent start to move forward. Also, please attach your current tune so we can analyze that if you havent done so already.

[Seek]

My thoughts on the cylinder head valve spring seat pressure likes to be in the 300 range with aftermarket heads. Sounds like your measurement of 150 is low even with e7 heads and stock cam but ill look into those specs further. Your rocker adjustment sounds good for your pedestal mount rockers. Pushrod length sounds correct. We might be getting lost with all the years of info and should concentrate on what is current. Fuel pressure of 33-34 may be too low with vacuum line on. Your combo may want more fuel pressure. Try taking the vac line off regulator and plugging it with a screw and drive the car with static pressure at 40 and see how the car and idle responds. Usually the tiny aftermarket screw in gauges arent very accurate for reading fuel pressure and make sure the schrader valve core is removed from the service port on the fuel rail if that is your source for checking fuel pressure. Your maf sensor is also a key component in dialing in a smooth idle. Forget about going carb, you will not be doing yourself any favors there. The cam being installed straight up or dot to dot vs advanced 2 degrees depends on if the cam has any advance built into it but normally should not result in rough idle. What is important is what your vacuum reading is at idle as that will be a key indicator to many things. You should have no less than 10 in. hg. at idle during normal if not all operating temps. I would recommend to avoid getting lost in translation and detail of years of different parts and settings for us to start from scratch with your current combination and tune and focus on that so we can try to tackle this rough idle issue. If your signature line is current and accurate, that is an excellent start to move forward. Also, please attach your current tune so we can analyze that if you havent done so already.

I think you may be getting lost between my posts and those from FoMoCo17. He has e7 heads, I have tw170's. I posted pushrod length. I'm not sure where you're getting a "150" from? Stock e7 head spring pressure is 90-100lbs closed. These being 130lb is already a bit higher than the factory heads. Not sure closed should need to be any higher - most springs included on off-the-shelf aluminum heads are 110-120lb. AFRs come at 120lb. For a stock HO cam, this should be more than enough.

From what I've read online, idle vacuum should be pulling 30-34psi fuel pressure, depending on how much vacuum there is. 16inHg sounds like it's supposed to be right at my 33psi area.

My signature is correct as of a few weeks ago. To troubleshoot this issue, weeks ago I changed the following:
24lb EV6 injectors, 75mm Pro Flow MAF to 19lb EV1 injectors, stock 55mm MAF

I've got the default GUF1/A9P tune files on there, from http://www.eecanalyzer.net/strategies . It runs the same as removing the Quarterhorse from the EEC completely.

From 15 minutes of running, the EEC-IV kept the KAMRF at 1.000 - the idle tune's fueling itself seems pretty dead on for 10+ minutes of closed loop. That datalog is further up in the thread.

[EDS50]

Ok good, im caught up now. Kamrfs will not start displaying until you put about 18 miles on the car if you have recently reset them or haven't been driving the car. The idle vacuum and fuel pressure vacuum i am discussing for my purpose is unrelated. Your idle vacuum reading will be a key indicator to your rough idle symptoms. Taking the vacuum line off the fpr and plugging it will tell you if the idle improves which would mean the engine is lean and wants more fuel and will also result in slightly better idle vacuum if that makes sense. This is an exercise to see what the car is telling you is going on and wants. Idle timing as cgrey8 discussed s another key contributor to idle quality which is tune related. I'm trying to cover the mechanical aspect of it first. Just my approach....

[cgrey8]

...I like the idea of controlling how far the spark can actually jump around ... what table or scalar do I adjust for this for an A9P?...

If using the open source GUF1 strat for BE, look for function(s) in the Idle group that also deal with Spark. I'm not at home to look into BE and give exact info at the moment. I'll TRY to remember to do that this afternoon, but I'm very likely to forget. If you don't figure it out, just let me know, but I think you'll be able to figure it out with this info.

I would also recommend calming down the Idle - ISC controls as well. From what I remember, the stock tune jitters it like it does spark to try to get "fast" idle RPM control. I calmed both down to determine what my engine's real need was. Then stared dialing them back in as I found a need. Once I was done, my adjustments weren't nearly as wide-swinging as they were in stock form.

...By the way, my computer was also sent out and repaired incl new capacitors etc.. Possibly the spark is jumping around from the previous adjustment by the computer...

Spark jumping around is datalogged from the tune. These older computers don't command, then "listen-n-report" what they actually got for spark. What you datalog is what it intended. So if what it intended got modified by old/faulty hardware, you'd never know it from the datalog. And generally faulty hardware doesn't fail with this presentation. Bad caps in the EEC, in particular, are not nearly so selective in how they cause problems.

...I’ve got it pretty much at 14.10 now for E10 gasoline...

I know a lot of people want to talk in terms of actual AFR. However doing so can be misleading and often causes more confusion than it clarifies. To keep things clear with minimal confusion, I recommend for people to refer to LAMBSEs and AFRs in terms of lambda instead of AFR. If you aren't familiar with the concept or maybe are familiar, but just have never wrapped your head around it fully, I've got a doc here that can help.
Widebands measure lambda (λ), not AFR.
I re-read through that link and tested some of the links to find many were defunct. So I updated the document and added additional info about the difference between the LSU 4.2 and 4.9.

[Paulie]

...I like the idea of controlling how far the spark can actually jump around ... what table or scalar do I adjust for this for an A9P?...

If using the open source GUF1 strat for BE, look for function(s) in the Idle group that also deal with Spark. I'm not at home to look into BE and give exact info at the moment. I'll TRY to remember to do that this afternoon, but I'm very likely to forget. If you don't figure it out, just let me know, but I think you'll be able to figure it out with this info.

FN841N and FN841D are the functions for spark adjustments at idle

[PDE]

When you had the engine redone, what machining was done.
1. Engine Decks cut?
2. Cylinder heads cut?
If this was done, then your lower intake manifold may not be sitting true against the cylinder heads. Even a slight cut on the heads and block deck can cause this to happen. If the intake manifold is not sitting square to the cylinder heads, it could be leaking and it is very hard to detect. The smoke machine was a good idea, but the manifold could actually be leaking from the valley side intake/head interface. I had this happen to me.
The aftermarket makes double thickness intake gaskets just for this reason.
Maybe you have already looked at this, but I thought I would mention this, it took me 3 years to figure this one out.
Good luck.