Author Topic: Help! Loosing IAC reference position after transmission swap  (Read 488 times)

Offline kiss2101

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Help! Loosing IAC reference position after transmission swap
« on: October 03, 2021, 12:26:52 pm »
Hi All,

I'm having a weird IAC problem that developed after I swapped my transmission - weird :o , and I would need some help if someone can give me an advice. 

Problem + symptoms:
It looks like that intermittently the IAC valve losing its reference position causing a high or low idle speed. The commanded steps are all good as per logs, but the car requires less or more (from pos 11 till 80) to idle at the same RPM. Everything else is the same MAP, in. PW, Lambda, Spark etc.. just the valve needs more or less.

- New IAC stepper valve, Ford 4 pin
- I thought it is a vacuum leak so intake was disassembled, re-surfaced, re-sealed, all the vacuum lines replaced and smoke tested.
- All the wiring checked and verified, Grounds checked and replaced with higher gauge wires
- Different configs, bench tested valve etc.. 

Possible problem source: As the problem appears right after startups even with the same config and conditions, I started to look into Cranking logs when I noticed that the Cranking wasn't recorded in the logs at all. There is a missing 2 second when happens (see below logs).

Note: The only thing that changed is the transmission and the starter motor (brand new bosch unit).

No cranking log:!AiGVmB9OpHfrgvdc_Yxd4XIT_lhP0A?e=YglaAN

No cranking log 2:!AiGVmB9OpHfrgvdd3sTnofGOK19_-g?e=CSWLOR
Cranking visible before swap:!AiGVmB9OpHfrgvdek4YRias6AeYJ8g?e=mmP5Fg

Would someone is able to point me in the right direction or tell me if I'm missing something?

Thank you in advance,

//I didn't want to write down all the things that I tried or config changes to keep it short, but please let me know if extra info needed//