F115 iac testing. Idle issues

[Andysuomi]

Hello.

I am a long time reader and very rare poster in this forum. I find there to be a lot of useful information contained within it though!

I have a 2005 f115 which has been running perfectly until this morning. I noticed when I started it cold in the morning that it didn't go through it's normal warm up high idle speed and was just trying to idle at it's normal speed (800ish rpm). I stopped the motor and tried re-starting it at which point it jumped up to it's high idle speed. The problem is now it is only idling at its high idle speed (around 1500rpm) even once it's warmed up.

After searching through a few forums it seems that this high idle speed is a common issue and can lead to ECM failure if left in attended. I connected yds and did the static test to which I could hear a VERY faint sound coming from the iac. How loud is this sound normally? I had to have my ear next to it to hear it. I also. Can't really hear it when I turn the engine off which I believe I should be able to.

After leaving the engine running for a few minutes I noticed that the iac was very warm (almost hot) to touch compared to the rest of the area it's in. Is it possible that this is sticking or is stuck and is hence heating up as it can't move? How does this part actually work? Also is there any way of cleaning it or checking it for operation when it's removed from the housing?


Sorry for such a long post!

Thanks in advance for your help and assistance! :-)

[rodbolt17]

its a simple stepper motor.
has two 12V inputs and 4 ground paths.
at key on 12V is applied to both.
the ECU applys the ground path in STEPS to rotate the motor left or right(pintle in or out).

its NOT monitored by the ECU for anything other than idle speed.

however if the idle speed is incorrect for the MAP,TPS and ECT inputs it trys to STEP the motor.

it will continue apply the ground attempting to make the engine idle according to the ECU map until it overheats the ECU.

at shutdown, you should hear a distinct rattle for about 2 sec.
this is the ISC resetting to the 100% position in anticipation of the next start cycle.
its also why EFI motors start fast and settle down.
even your EFI car does it.
they typically are rather warm but we find anything over about 200*F means they are done.

[Andysuomi]

Hi Rodbolt.

Thanks for getting back to me.

I have pulled the IAC out of the motor and have noticed that is has a fair bit of black stuff on it. Is there anything that I can use to clean it? I have conducted the resistance tests on the IAC and it all seems ok. Would it be ok to run the static tests on the IAC with it removed to check that is is/isn't moving?

Thanks,

[Tony Harper]

hi guys, I have a similar prob with a 2002 F115 aet, did you get yrs sorted out, cheers Tony