Help with the IAC

[hear]

I'm having trouble figuring out an IAC problem. The jeep is idling SUPER high, and I'm pretty much convinced at this point that it is sucking excessive air through the IAC port in the throttle body. I've bench tested the IAC...well, really I've verified that the stepper motor does its thing when you vary 12V/ground across the different pins. I have not exercised the entire travel of the IAC, but we've put in several including a known working one but nothing changes.

Removing the IAC from its home but leaving it plugged in also doesn't change anything. The IAC is fully drawn in, and running the jeep you can see the IAC plunger isn't moving.

Testing the voltage at the pins, I'm getting +/- 0.6V at some of the pins & 0.15V on some other combinations with the key on. We tested against another jeep and we see 12V at the plug, so it feels like the problem is right in there. We've verified continuity from the plug to the various pins at the PCM.

It seems like the PCM isn't supplying 12v to the IAC plug. But THAT is hard to verify.

I'll add that this is a fairly new PCM from @Wranglerfix so I wouldn't expect it to be the source of the problem. But I'm out of troubleshooting ideas.

 

[hear]

We're also getting a P0505 Idle Control System code. The throttle body has been THOROUGHLY cleaned, which I'm sure somebody will suggest. The issue is that the PCM doesn't appear to be supplying 12V to the IAC stepper motor.

Has anybody run into this before?

 

[Mike_H]

I'm having an erratic idle issue (slow) and Blaine suggested the clockspring...the ground for the 5v signal for the TPS goes through the clockspring. Don't know if its related or not, but if you can do an A vs B swap, the Clockspring is relatively easy to swap.

 

[hear]

I'm having an erratic idle issue (slow) and Blaine suggested the clockspring...the ground for the 5v signal for the TPS goes through the clockspring. Don't know if its related or not, but if you can do an A vs B swap, the Clockspring is relatively easy to swap.

The wiring for the IAC goes directly to the PCM without any splices. The other sensors all share grounds and 5V supply, but the IAC works vastly differently than the other sensors. For some reason the computer just isn't putting any voltage/ground on any of the IAC pins. I'm not saying the clockspring aint the problem, but I have good ground & 5V at all the other sensors.


And the high idle (which is why we were even looking at any of this) is definitely the IAC. We took another IAC out of a running jeep (which had its IAC valve thingy partially extended) and put it into this jeep w/o connecting the plug. Ran like a dream. I need to better understand what the IAC does after the jeep is warmed up, and also what it does during normal driving, although none of that helps me actually solve the root cause here.

 

[hear]

Bumping since everybody wanted to discuss this in my "bench test PCM" thread.


See also: https://wranglertjforum.com/threads/bench-test-pcm.72989/

 

[hear]

Paging @Wranglerfix

Have you ever seen a PCM stop sending good signals to the IAC? Especially on one of your units? Or any specific tests we can perform to isolate the cause?