Resolved High Idle - Passed BLT

[TurboTesh]

I know there have been a million threads on high idle, but I can't seem to pinpoint mine

Can someone point to the likely culprit so that Im not on a total wild goose chase? I've done a boost leak test, sprayed for leaks around IM, loosened throttle cable, and checked Vacuum lines.

Another symptom is that I can screw the BIS all the way in and it does nothing. There is a point where it will raise idle, but never lower than 1200RPM. IAC was replaced, because my other one went wacky and jumped around on me when warm... but idled the same as now. TPS was checked when throttle body was off over winter, and was tested and adjusted. ECU says the throttle position is at 0 when at idle.

The weird things is when I turn on my A/C, and the fan comes on... the idle goes to a perfect 850-900 rpm. As soon as it turns off, it goes back to 1200. While driving it hovers around 1500 at a stop sign. This makes me think it's electrical and thus why i posted it here.

Thoughts? Is it a maladjusted IAC that can cause all this grief?

 

[Kpro22]

You might have air still inside you're system .

 

[spyderdrifter]

Have you replaced your throttle body shaft seals ever? Those are a potential culprit that you probably won't see doing a BLT. Even your TPS could be out of range and is leaving the throttle plate open a little bit. Also check the FIAV gasket on the bottom of the throttle body. A bad IAC could cause this, but there's really no adjusting them since the plunger inside moves when the ECU tells it to. The BISS should be the last thing adjusted when tuning your idle, but all of us including me are guilty of turning it when we really shouldn't be.

 

[TurboTesh]

Hey spyder, thanks for chiming in. I changed most of what you listed already. Solution was actually found in a separate but related issue I had.
http://www.dsmtuners.com/threads/whats-this-noise.512590/#post-153652613

My new Valve cover didnt have a PCV, and the nipple was too large. Without that restriction in size, my intake manifold was drawing in too much air from the crankcase in low rpm vacuum conditions.

 

[PlanZero]

Just to add: AC will always make it drop if you're still using the puny OEM 75amp alt. Upgrade to a 90amp.