Do you have the park/neutral switch connected to the ecm? Do you also have a speed sensor connected and the ecm able to see the vehicle speed? Either of those signals being absent can cause a high idle after coming to a stop. A engine stop/restart resets the IAC position.
any play in the throttle shaft?
Originally Posted by tayto
I bought a TBI from this place when I rebuilt the motor/driveline ~5 years ago.
https://www.sprperformance.com/
The injectors that came with it failed after a year. The pedal always feels stiff off idle even after replacing the cable.
In the past I have pushed and pulled on the shaft while the truck was running thinking if there was play i could affect the rpm but it never made a difference.
If the shaft was loose it would just idle high? not add the IAC counts?
I just replaced the park/neutral switch again because i had no reverse lights. It wasn't that old. It has always been hooked up.
The truck is an 89 and came with the 400 turbo. It has the little green box behind the dash. It is no a 4l80 using a MSD atomic controller.
When i drive the truck next I will run ALDL and check for speed data.
Yes I have had throttle bodies where the shaft is loose and causes high or surging idle. i'm 99% sure SPR rebuahes all their units so I wouldn't worry there. FWIW, a '7427 pcm (or '7060) would have controlled your TBI and 4L80E.
I have the $4F mask. At the time i was not confident about installing and possibly repinning a different ECU. If this continues i might try going with a different unit.
I have a CJ build i can use the MSD with.
I dislike unsolved threads so i wanted to post, It has been a month and the truck has been running perfect and not one instance of high idle. I guess i will leave as is for now.
If I ever figure it out I will post the solution,
Chris
Hello all,
The issue is back today and more consistent. When it idles high i don not have Idle/cool flag
high idle flag.JPG
when it idles normal I have the Idle/cool flag.
normal flag.JPG
Any idea what this means? This time at high idle my IAC counts were only 56. but going from reverse to drive the RPM shoots up. Other than re-pinning a better ECU any options?
Possibly solved,
Just in case someone reads this in the future i may have found the culprit. I came home the other day with the high idle, before anything else I grabbed the laptop and data logged.
The TSP data was jumping around from ~.4 to .9 at idle. Resetting the key the ECU starts with a new voltage reading and idles ok. When it starts fluctuating the IAC gets confused? The TPS test ok, It operates smoothly from .54 to 4.7 volts but when it got hot enough it would act up. Not with rhythm, just a blip here and there. Unless you sit and watch the data you would never catch it.
Anyway, tossed another TPS on it and for now appears to be ok.
Chris
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