RB20 high idle issue.

[Voodoo_ChildR32]

Just swapped out my turbo, cam seals, and IAC valve. Now when I start my car first thing in the morning it starts then the rpms slowly climb to 1500 and stay. If I drive the car my idle goes to normal. If I let it sit it idles high for about 5-10 min then slowly returns to normal. Never had this happen before, anyone else's car do the same?


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[TheyKilledKenny]

Could be TPS, AACV, ECU, vacuum leaks, Timing (CAS 15 deg BTDC), MAF, or the new IACV. My car was doing this kind of crap when my MAF was playing up.

[nismocan]

I would go over your IAC connections as you just put it in, give it a good clean and make sure it is sealing properly(gasket). If not that then check your AAC as it could be malfunctioning allowing to much air in. Just my 2 cents worth.

[Voodoo_ChildR32]

Ok, story so far....
I have changed out the IAC, AAC, PCV Valve, Checked vac lines and replaced clamps, Replaced coolant temp sensor, Checked TPS voltage (0.46v @ idle), adjusted IAC screw all the way (no change), Checked for intake leaks, and still idle at 2000rpm.
The only way I can get a normal idle (800-1000rpm) is to unplug the IAC valve connector and run that way. The second I plug it back in my rpm's jump instantly to 2000rpm. If I unplug the AAC valve there is no change.
This has got me totally stumped, googled the **** outta this topic, tried everything and still no luck. Even went as far as to clean both valves before installing them so I know they are clean. MAF has also been cleaned and resoldered.

[92GTSTproject]

set screw on the iac valve?

[Voodoo_ChildR32]

set screw on the iac valve?

Playing with the set screw doesn't affect it at all. The way to set it is with the IAC unplugged anyhow. I can run the car with the IAC unplugged, just has a little trouble starting when cold. The car runs like a top with it unplugged, got a rock solid idle. I guess I'll just leave it unplugged till I can find a fix.


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[TheyKilledKenny]

James, I had the same problem when my MAF was acting up. Lemme know if you wanna test my MAF in your ride.

[Voodoo_ChildR32]

Not sure if it's a maf issue, the car runs and boosts perfectly, just seems like the IAC and AAC valves are conflicting somehow. I did a BG fuel flush right before the issue started, I've read that some ppl have issues after carb cleaning due to the built up crap being removed and allowing more air to flow past the throttle plate. I rechecked my TPS and it's bang on.


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[Skym]

From what I understand, if got carb cleaner near throttlebody butterfly shaft seals, it probably stuffed the seals and created an airleak. Same problem on RB26 intake manifold when cleaning throttlebodies incorrectly.

If rpm stays up, then returns to normal, that from my experience usually means a airleak near throttlebody (air feed to IACV and AACV is next to throttlebody). Sometimes the rubber intake hose joiner on throttlebody has gone hard due to engine heat and doesn't seal properly (silicon intake hose joiner, new stronger intake hose clamps fixes the problem).

When my car had the MAF problem it idled at 1500rpm all the time when cold and warm. Also had MAF error code on ECU. Found out the MAF was stuffed and no soldering was going to fix it. Replaced MAF and cleared MAF error code on ECU, problem fixed.

In some cases the IACV can be the cause due to not being closed when engine is warm and swapping that out fixes problem. It has happened to few cars on GTRC in the past if you search forum. Another cause could be due to gasket on AACV wasn't replaced.

PCV valve could be another cause.