Random IAC opening...Gremlin!!

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Vortech347
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Random IAC opening...Gremlin!!

Post by Vortech347 » Thu Apr 25, 2019 10:45 am

Hardware that's new and/or double checked.

TPS sensor, IAC Valve assembly. I've gone through two of each....
All plugs/connectors associated with 10pin, TPS, and IAC... Pins are good, wiring is good.

Problem...

I've had this happen while warming up or just cruising around town. The car will on it's own go up to 2100ish-rpm. Pretty much just feels like a run away cruise control. It's fantastic... The car never recovers from it. I let it sit once when I got home for about 5 minutes and it never came back down. However.... if I just flick the ignition key while driving or pull over and restart it totally goes away. I've driven the car for 2 weeks, doesn't happen. Then randomly one day it happens. I haven't discovered how to replicate it so just having my laptop in the car logging all the time is a pain in the ass. Other than that IAC functions are absolutely perfect, no idle hunting, stalling, ect.

Is there anything I can look at in my tune to see if for some reason my car is commanding this? I did read once someone mentioning that if the IAC gets commanded too high it can get stuck? But then why would the ignition reset fix it....

At my wits end. Enclosed are some shots of a few things.
Attachments
idle3.PNG
idle3.PNG (8.99 KiB) Viewed 1065 times
idle2.PNG
idle2.PNG (13.2 KiB) Viewed 1065 times
idle1.PNG
idle1.PNG (8.85 KiB) Viewed 1065 times
Matt
90 GT, 347, Vortech Si-trim (11psi), Edelbrock 6037 heads, Super Victor 8.2 EFI Ported, 80MM Pmas, 60lb EV14 Bosch Gen 4 Injectors, KB BAP, B31 Cam, T56. Tweecer RT, A9L. Software: EA/BE. 550rwhp & 513rwtq.
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Re: Random IAC opening...Gremlin!!

Post by Paulie » Thu Apr 25, 2019 11:37 am

I doubt it is in your tune. I know it's a pain but I would datalog TS, ISCFLG, TP, RATCH, ISCDTY, DSDRPM and DASPOT. What I think you will find is ratch drops below the normal TPS closed throttle value and you get stuck in dashpot mode.
1990 Mustang 5.0, HCI, Vortech S-trim, FRPP 42# inj., PMAS MH95, A9L, Moates Quarterhorse, BE/EA, Innovate LC-1.

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Re: Random IAC opening...Gremlin!!

Post by Vortech347 » Thu Apr 25, 2019 1:08 pm

Ratch is what the computer remembers as my true idle voltage (location of TB) as read by the TPS correct?

When I set my TPS sensor here's what I've done.

At operating temp I disconnect the IAC and use the throttle stop screw to get my idle at where I'm commanding. Then plug the IAC back in. I then turn off the car and rotate the TPS until it's at .98 while logging with key on engine off.

I took my laptop with me for a 45 min drive in stop and go city traffic. Of course because I have the laptop it's going to run fine. grrr
Matt
90 GT, 347, Vortech Si-trim (11psi), Edelbrock 6037 heads, Super Victor 8.2 EFI Ported, 80MM Pmas, 60lb EV14 Bosch Gen 4 Injectors, KB BAP, B31 Cam, T56. Tweecer RT, A9L. Software: EA/BE. 550rwhp & 513rwtq.
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Re: Random IAC opening...Gremlin!!

Post by Paulie » Thu Apr 25, 2019 1:50 pm

Yes ratch is what the computer thinks is closed throttle voltage. What typically happens is the TPS voltage intermittently goes low from either a sensor or wiring issue and the computer thinks that low voltage reading is now closed throttle voltage. So now when the issue goes away and you are back at your original closed throttle voltage, the computer actually thinks you are at part throttle and stays locked in dashpot.
1990 Mustang 5.0, HCI, Vortech S-trim, FRPP 42# inj., PMAS MH95, A9L, Moates Quarterhorse, BE/EA, Innovate LC-1.

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Re: Random IAC opening...Gremlin!!

Post by jsa » Thu Apr 25, 2019 5:41 pm

Dashpot decay rate, lb/min - 0.0012 followed by bigger numbers.
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Re: Random IAC opening...Gremlin!!

Post by Vortech347 » Fri Apr 26, 2019 4:10 pm

Paulie wrote:
Thu Apr 25, 2019 1:50 pm
Yes ratch is what the computer thinks is closed throttle voltage. What typically happens is the TPS voltage intermittently goes low from either a sensor or wiring issue and the computer thinks that low voltage reading is now closed throttle voltage. So now when the issue goes away and you are back at your original closed throttle voltage, the computer actually thinks you are at part throttle and stays locked in dashpot.


Hmm...I'll get the meter out and check the wiring and connections more.


jsa wrote:
Thu Apr 25, 2019 5:41 pm
Dashpot decay rate, lb/min - 0.0012 followed by bigger numbers.
So the bottom two cells having more is an issue?
Matt
90 GT, 347, Vortech Si-trim (11psi), Edelbrock 6037 heads, Super Victor 8.2 EFI Ported, 80MM Pmas, 60lb EV14 Bosch Gen 4 Injectors, KB BAP, B31 Cam, T56. Tweecer RT, A9L. Software: EA/BE. 550rwhp & 513rwtq.
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Re: Random IAC opening...Gremlin!!

Post by Vortech347 » Sun Apr 28, 2019 8:48 pm

I adjusted the bottom 3 cells of my dashpot to .0012 So far so good. Actually smoothed some shift timing issues for drivability out.

I drove about 70 miles today with it and a few heat cycles. No problems. I check back in a few weeks to update this.
Matt
90 GT, 347, Vortech Si-trim (11psi), Edelbrock 6037 heads, Super Victor 8.2 EFI Ported, 80MM Pmas, 60lb EV14 Bosch Gen 4 Injectors, KB BAP, B31 Cam, T56. Tweecer RT, A9L. Software: EA/BE. 550rwhp & 513rwtq.
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Re: Random IAC opening...Gremlin!!

Post by Vortech347 » Mon Apr 29, 2019 1:35 pm

Well damn it. It happened again taking the kid to school.

I was idling at a very long red light. RPM was fine at it's normal 750 then just slowly raised on it's own to around 1700. I drove it the next few miles like that but it never went away until I turned the car off. DAMN IT!!!!!!!!!
Matt
90 GT, 347, Vortech Si-trim (11psi), Edelbrock 6037 heads, Super Victor 8.2 EFI Ported, 80MM Pmas, 60lb EV14 Bosch Gen 4 Injectors, KB BAP, B31 Cam, T56. Tweecer RT, A9L. Software: EA/BE. 550rwhp & 513rwtq.
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Re: Random IAC opening...Gremlin!!

Post by ironmanisanemic » Mon Apr 29, 2019 3:37 pm

Had something similar happen myself, it wasnt exactly the same but close enough.

First, its a waste of time to "adjust" the TPS. The ECM uses the lowest Voltage measured as "RATCH" and subtracts that from the actual voltage to get a relative voltage. Ratch can get lower but cant come back up without an ECU reset, so if you start the car with your foot on the throttle, the TPS value may be 1.25v and the ECU will set that to RATCH. As soon as you let off, whatever your TPS voltage settles to is now the current RATCH value. Most functions in the ECU reference relative TP Voltage instead of actual TP Voltage. So if something causes ratch to fall lower than normal it may cause other issues.

Second, with how the TPS works out of the way, it does sound as if something is causing RATCH to be set to a lower voltage than your TPS can go based on your setup, causing your engine to go into PT and Dashpot. What you need to do is drive and datalog at least what was mentioned above. Observe what your TP actual and TP relative. When you start having the high idle issue, if tp relative is higher than 0.0v this is where your problem is.

Third, if this is your problem the only way that ratch could be registering lower than what your tps is set to is if there is a short to ground somewhere on the tps signal wire or within the tps itself. It could also be that you could have a short to power causing a phantom high tps reading, but shorts to power are a lot less common than short to ground.

Ive personally had a bad TPS that had an intermittent short inside itself that would cause the ecu to default to failed tps settings and use a preset tps value of 1.27v no matter what. In my case it was very random like yours and it would cause a check engine light along with a high idle. While i was trouble shooting this i also had found a few breaks in some wiring insulation inside the harness that may have been contributing to my issues as well. So just because you show continuity end to end doesnt mean you may not have a short to ground even an intermittent one.

I hope i was somewhat helpful

*EDIT*

Just for reference, the transition to part throttle according to the TPS in CBAZA is 0.04v relative throttle position. so as you can tell it wouldnt take much of a deviation of ratch to skew the calculations off and push the ecm into PT even if you are at an idle.
1989 Ford Bronco:
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Re: Random IAC opening...Gremlin!!

Post by Vortech347 » Wed May 01, 2019 5:20 pm

Thank you for the info. It's weird that it did it straight from idling on it's own with no pedal input. I'm on my 2nd replacement TPS sensor. Guess I'll have to really start chasing wires. I tugged on all of them pretty good while I was checking voltage and resistance. I've got a wiring chart somewhere for that harness. I'll see where it's grounded and check that.
Matt
90 GT, 347, Vortech Si-trim (11psi), Edelbrock 6037 heads, Super Victor 8.2 EFI Ported, 80MM Pmas, 60lb EV14 Bosch Gen 4 Injectors, KB BAP, B31 Cam, T56. Tweecer RT, A9L. Software: EA/BE. 550rwhp & 513rwtq.
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Re: Random IAC opening...Gremlin!!

Post by Paulie » Thu May 02, 2019 11:30 am

Do you have the 10 pin extension harnesses installed? I had a similar issue years ago. After I installed the extension harnesses the problem has never returned.
1990 Mustang 5.0, HCI, Vortech S-trim, FRPP 42# inj., PMAS MH95, A9L, Moates Quarterhorse, BE/EA, Innovate LC-1.

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Re: Random IAC opening...Gremlin!!

Post by Vortech347 » Thu May 16, 2019 10:40 am

I don't, with my setup the extension harness is no longer needed.
Matt
90 GT, 347, Vortech Si-trim (11psi), Edelbrock 6037 heads, Super Victor 8.2 EFI Ported, 80MM Pmas, 60lb EV14 Bosch Gen 4 Injectors, KB BAP, B31 Cam, T56. Tweecer RT, A9L. Software: EA/BE. 550rwhp & 513rwtq.
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Re: Random IAC opening...Gremlin!!

Post by Vortech347 » Thu May 30, 2019 10:56 pm

Update....

While driving the car today for a short trip the gremlin struck again. Car went right to 1500rpm. I had time so I pulled off into a parking lot and jiggled the wiring to the TPS. Like a miracle the idle dropped down to where it should. Usually it takes an ignition reset to clear the issue. Looks like a wiring issue for sure. I'll trace the harness back as far as I reasonably can and replace that wiring and get a weather proof 3 pin connector setup to replace the aging original one.

Thanks all!!!

Btw, if I want my engine to drop RPM slower in between my shifts I want LB/min on the right of the scalar less or higher? My RPMS fall like a rock and my shifts have to be very quick unlike my 2003 Cobra.
Matt
90 GT, 347, Vortech Si-trim (11psi), Edelbrock 6037 heads, Super Victor 8.2 EFI Ported, 80MM Pmas, 60lb EV14 Bosch Gen 4 Injectors, KB BAP, B31 Cam, T56. Tweecer RT, A9L. Software: EA/BE. 550rwhp & 513rwtq.
2003 Sonic Blue 03' Cobra 497rwhp 481tq, Pro Racer Pack
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Re: Random IAC opening...Gremlin!!

Post by Paulie » Sun Jun 02, 2019 10:28 pm

Vortech347 wrote:
Thu May 30, 2019 10:56 pm
Btw, if I want my engine to drop RPM slower in between my shifts I want LB/min on the right of the scalar less or higher? My RPMS fall like a rock and my shifts have to be very quick unlike my 2003 Cobra.
Lower numbers in the right column will cause the RPMs to drop slower
1990 Mustang 5.0, HCI, Vortech S-trim, FRPP 42# inj., PMAS MH95, A9L, Moates Quarterhorse, BE/EA, Innovate LC-1.

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Re: Random IAC opening...Gremlin!!

Post by cgrey8 » Mon Jun 03, 2019 5:16 am

2 other things to consider modifying in the tune:

DNPPM to bump the ISC open when you transition from drive to neutral.

and

Adjustments to both DASMIN & MINMPH. DASMIN will hold the minimum DASPOT so regardless of ramp-rate, the value won't go below some value. And the MINMPH will set the RPM at which DASMIN is no longer holding the minimum, and idle RPM control goes closed loop.

See if making adjustments to those things don't improve things a good bit.
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Re: Random IAC opening...Gremlin!!

Post by Project Reef Blue » Wed Jun 05, 2019 2:40 pm

FWIW I had a similar problem last year and it was TPS and RATCH related after swapping to a 90mm throttle body. For whatever reason TPS voltage at closed throttle would increase once I drove the car around. After 15-20 minutes the car would idle as you described. Because the TPS closed throttle voltage was higher than when I had first started the car (RATCH) the computer would get stuck in part throttle mode and not return to an idle. Advice from EFIdynoTuning helped me. Adjusted RATIV upto 1.5 and problem went away. Good luck !
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