Couple days ago I took the car out for a spin. I floored it in 4th and heard a pop like fuel cut. I looked on my zietronix’s guage and max boost registered at 32.1. I’m thinking that was just a fuel cut. When I got home, the car idled at 2000 rpm. I shut it off thinking I’ve blew a vac line as it has happened before. I checked all vac lines and everything is intact with zip ties on every vac line. I then did a boost leak test, it’s holding boost so I eliminated vac leak. I then did compression test. All cylinders were with in reason. 140’s to 150’s. I then swapped out the stepper motor since I run meth thinking I may have fried it. It looks normal and didn’t look like it was fried but swapped it out for one that was working. Still having high rpm idle. I then cleaned out the throttle body and the MAF, also changed and replace spark plugs. Still same result. I swapped out the ECU and tried a different one and no change. I’m thinking this could be a MAF issue. I don’t have one to swap in yet. What else can cause high idle. I did some logging with Evoscan and the only thing that looked out of sync is the EGR temp. The temp seems higher at the same rpm compared to when it was running normal. Would a malfunction EGR cause high rpm idle? Any help is appreciated. Thanks

 

No help?

 

IAC (idle air control) could be stuck or not working...?

 

hmm mine has been doing the same, except mine happens when i just start it up... dnt really know what it could be

 

sounds like you had an explosion of some sort.

some tb's i get in have suffered from some type of plenum explosion / fire....this is evident on 03/04 tb's that have this plastic flapper that lives within the idle air circuit.

did you inspect the iac? take it off the tb, turn on the ignition. you should see the iac move.

maybe the biss screw is fried / charred:


inspect the throttle blade, maybe it was bent a bit...something common with nitrous backfires.....

 

Mine has done this before.

My car sat down for about a year 1/2 before i bought it. It would start up and idle real high 2k nothing more or less. Drive the car hard and it would get hott and eventually it would go down and sometimes i would just be driving and then come to a stop and idle high at like 2k. after a while of starting the car and the IAC working and moving it doesnt happen. I would say double and check the IAC it more likey to be that in both or you guys situations.

 

Thanks for all the replies guys. I've change the stepper motor (IAC valve). Both looked good. It could be the bliss screw as Aby@MIL.SPEC mentioned. I'll check that when I get a chance.

 

Wow is that really what the BISS screw looks like? I bet i could just machine one out of brass.

 

^ they are ~$2.50 from the dealer!

 

I took the bliss screw out. It was slightly burned at the tip. Replaced it with a new one and still same results . I'm going to have to crawl under the car and check every line that goes into motor. What happens if the MAF failed? Would it cause high idle?

 

If the MAF failed you would be getting a cel for one and a rough rough rough idle.