I have searched and didn't see anything quite like this. Should be simple for you guys. Rebuilt engine with mods listed below.Also new ignition coil,Borg Warner. Was doing this before the engine though. Idels just fine at start up. While driving though when coming to a stop the rpms stay at about 2k untill I come to stop then drops back down to about 900. Doesn't matter if cold or warmed up. It started doing this when I did the headers. I also at the same time descreened the MAF. Any suggestions? All other sensors are original with 140k except for oil pressrue and block temp sensor. I appreaciate any ideas.

 

IAC, remove it from the TB clean it off and put it back in. Usually that's what will cause a high idle.

 

thanks for the advise

 

After I cleaned my TB I started getting rpm hang. Dabbed some oil on the butterfly rod where it enters the TB housing; cured the issue.

 

Don't have a Holley TB by chance do you? They are notorious for the return spring not being tight enough to close the blades while the engine is pulling alot of vacuum like when coasting.

 

Sounds like a possible vacuum issue?

 

sometimes when you remove some of that sludge in the TB you'll need to readjust the idle screw. My car was doing the EXACT same thing and thats all it took.

 

I took the IAC out last night and cleaned it as well as the hole in the bottom of the TB.Drove to work this morniing and still doing it. I don't think vacum problem as car was doing this before new engine when all vacum was hooked up in original location and it hasn't worsened. Stock TB also and spring seems tight. My buddy works at goodyear and we hooked it up to the scanner and it came back driver side 02 sensor out. Would this cause it maybe?

 

A bad O2 sensor won't cause the rpms to hang.

 

might be a stupid question but how do you adjust idle spring and where is it? ar you refering to the spring that opens the throttle blades? How would that be adjusted?

 

There is a bolt on the drivers side of the TB, you may need to remove the throttle linkage cover to see it. You'll need an allen wrench. That is all I had to do with mine, exact same symptoms. Fix that O2 sensor!!

 

Was the car in closed loop when you scanned it? If not, the O2's might not have been warmed up, and wouldn't be reading right.

Did you have your PCM tuned?

Dan

Dan

 

Yes sir Josh I will fix that 02 ! Car had been running for 15 min and driven when we tested the 02. Thanks for the advised though.

Yes computer is tuned for all delete air and egr and mods. No reason to beleive computer is problem because every other Mod I requested is working perfectly. no skip shift, fans on at 185 and no other codes were thrown so I don't think is computer issue. Going to try Josh's suggestion and hopefully fixes. Thanks to all for help. Will post with results