Confusing Idle Problem...

[LoserCard]

I know that there are a million and a half threads and after half a day of searching I am trying to come across a definitive answer... So here is my problem and it is very specific so I would hope that it would be solved soon. I have a hunch on what it is, but I would like a second opinion.

First off, my car idles just fine at 700 RPMs with everything plugged in. When I go to adjust idle, I disconnect my TPS harness and my idle jumps all the way up to 1500 RPMs. ALSO, my IACV idle screw is screwed all the way in. Is this 100% a IACV problem or should I look else where before replacing it? I read on a few threads that it could be my temp sensor, however, my interior gauge work just fine.

So if it is my IACV, should I go to a junkyard and find a used one, or should I dish out $150 for a new one? Is there any way to test or repair the one I have? I have cleaned it before, but I didn't know how to test to see if it was operating properly.

EDIT: I found the thread on how to test the IACV's electrical components. So I have another question: Do these things just die? Because I haven't done much to it since the last time I had to smog and they checked the idle.

[alms24sebring]

I dont understand the question? If it was idling fine then why try and find a problem. Is it rich?

Other than that an IACV is pretty simple. You can take it apart and clean it but be sure not to lose the spring and plunger inside. Alot of times you can clean it by spraying a crap load of brake cleaner through it when its off. Usually they hardly ever just die. If you put 2 alligator clips on each prong and touch it to the battery quickly, you should hear the click. Also just suck on the metal vacuum connection to make sure it is sealed properly internally. Also put a fresh gasket on it, rtv will work since its not under pressure.

here's more info
iacv-aac-cleaning-and-testing-tutorial-t251133.html

As a side note, there are 2 temp sensors. One is for your dash and the other is for the ECU. Its just a resistor and it is like $3 so its worth it if you wanna try it.

[LoserCard]

It idles perfect with the tps plugged in, but I recently needed to correct my timing so when I went to do my timing I found out that it idles at 1500 with the tps unplugged.

[alms24sebring]

Sooooo.... leave it plugged in? Am I missing something?

It might be a failsafe when a TPS goes bad to idle high instead of bogging out and dying, but Im just guessing.

[LoserCard]

Well I went to go smog and he wont pass me because he can't check my timing because of my high idle with the tps unplugged.

[alms24sebring]

ok so let me get this straight. You failed emissions. You try and check/correct the timing in hopes of running cleaner. Still not clear why the TPS is unplugged in the first place is what Im getting at. Plug it in and check the timing??? Im so confused, I need more background info in what you are trying to do.

[corn322]

Where do you live where they check your timing during the inspection?

What (if any) engine mods do you have installed?

[OutToWinPAHC]

ok so let me get this straight. You failed emissions. You try and check/correct the timing in hopes of running cleaner. Still not clear why the TPS is unplugged in the first place is what Im getting at. Plug it in and check the timing??? Im so confused, I need more background info in what you are trying to do.

the correct way is to get the motor to operating temp and unplug the TPS to set the timing. This causes the ECU to lock timing electronically. This is how the FSM indicates, now I don't know of states that check it unless it failed and they are now being paid to correct it.

[alms24sebring]

Thank you, that was the answer I was looking for.

[LoserCard]

Ok here are the tests that I have performed and I think I may have narrowed it down to my engine temp circuit or air regulator.

Test 1: Removed IAC and inspected and tested solenoids. PASS
Test 2: Unplugged IAC, FICD (AC Solenoid), TPS, and WOT sensors. Set idle to 700, set timing to 20BTDC. Idle screw screwed in about 1/4 inch (air regulator stuck open?).
Test 3: Plugged in TPS and WOT sensors. No change.
Test 4: Unplugged TPS and WOT sensor, plugged in IAC and FICD. Idle back at 1500 rpms.
Test 5: Unplugged engine temp sensor (ecu sensor), idle still at 1500.

So I am really considering that it is my air regulator valve because:
A. With my IACV not operating, my idle screw is almost completely closed. Meaning air is coming in fast from somewhere.
B. With my IACV operating, it seems like it is in an idling position except twice the amount of air is being let in from the air regulator.
C. I know this fact may not prove much, but I can lower my idle by squeezing the air hose that runs to the IACV and air regulator from the air intake hose.

So with all that, you think you guys agree that my air regulator is dead or do you think it might be my engine temp sensor circuit?

[LoserCard]

Engine temp circuit passed. So I guess that just leaves air regulator. I will have to source on of those out and wait to see if that fixes my idle.

EDIT: I was able to partially squeeze the air regulator hose and it dropped my idle slightly so I am thinking my air regulator is just worn out and stuck in the open position. Although I am still confused why my idle is perfect with the TPS plugged in. Does it detect that my idle is high so it closes the IACV?

[OutToWinPAHC]

Well there are more then one AICV's in sense. One for idle, one for fast idle the ecu is just controlling them. If it were bad the TPS shouldnt let it drop so much. I wonder if you have unmetered air of if the throttle plate is cracked open it should be 100% closed

[LoserCard]

Alright guys... I have a very weird situation now. If I block off the hose that runs off the intake to the IAC and air regulator JUST ENOUGH to lower it to lower my rpms for a little bit and unblock it, my rpms stay normal... I have cleaned my IAC, but does it need to be greased or something? Maybe the spring that returns the plunger to it's normal closed position is worn out? I am seriously confused now.

[LoserCard]

Oh yeah and my air regulator does work because I blocked it off completely and my idle was still 1500. No vacuum leaks that I could find with water or parts cleaner. Outtowin, I am 100% sure my throttle plate is completely closed. Signs are pointing back to my IACV or it's circuit.

[Ciscog20]

Did u ever figure out what was wrong? My 99 g20 is ding the same issue at timining/ idle adjust.