I've had a couple weird issues that I don't particularly understand. Any input would be greatly appreciated!

When I'm coming to a stop at a set of lights/stop sign the engine revs up and when I come to a complete stop the engine drops back to regular idle. So it revs right up to 2200 coming up on the stop, and then idles after you've completely stopped.

The other issue/annoyance I have is when I rev up my motor it takes quite a while for it to drop back down. It stays there for longer than I'd like, it only does this after being warmed up. If the car is cold neither of these problems are apparent.

Any thoughts? Someone on another forum mentioned something about the brake booster? How hard would it be to replace one of those (if that was the cause).

 

Do you have any modifications done to the vehicle?


I would first check the throttle body; GM electronic throttle bodies are know for idle issues due to carbon buildup in the throttle bore.
If you clean it out, be very careful to not get cleaner in the IAC and the other sensors on the throttle body.

 

Well we have no IAC so no worries there. Clean your TB and MAF and try a new air filter, ashould work until it all gets dirty again.

 

well, physically there is no IAC; but since idle is controlled by the TB motor/pcm...you can still get **** in there.
I have seen several $200+ fuckups because of spraying too much cleaner into them.

So just be careful. Spray your cleaner of choice on a rag, not directly onto/into TB

 

Ive doused mine with cleaner. Just make sure car is off or better yet unplug the TB

 

I cleaned the TB just today, will see if that helps at all. Wasn't very dirty, but might make a difference. Otherwise it has a 2.5 exhaust system catback (local bent/welded for me) and recently did the airbox mod.

 

What year? This is an irritant with my 08 2.4 manual. Unfortunately, it appears to be normal. My car is tuned, and the tuner hasn't be able to eliminate it.

 

It's a vacuum leak, check to make sure all your intake pipes fit together cleanly and aren't letting air in. If they are and your still having the issue it's either the throttle body gasket or the intake manifold gasket that seals to the head. If you have a 08+ with the two piece manifold, it technically could be that seal but I've never heard of that happening.

 

the throttle body cleaning seemed to help. as for the revving it seems to take longer for the motor to slow down in neutral.

 

Clogged cat and plugs and Tb clean needed.

 

well ****; if your just gonna throw a bunch of parts at it...We might as well go with battery, coils, power steering flush(gotta get them bad electrons out), struts, engine, transmission flush, cap, rotor, adjust the points, front pads+rotors, alignment, wash car.


but really; before you condemn parts, you need to diagnose them...
How is the car driving Ardy?

 

I had this since I got the car, then still had it with k&n intake and still have with the turbo.
My car normally does it after rolling for a long time, like road trip or 20-30min trip. And rarely random.
I have not check any of the gaskets on the tb or manifold. But I did change my tb with a brand new one and did not fixed it.

 

i get it every once and a while also... i have the lsj tb though, and yes my car is tuned. it dosent bother me that much

 

Sorry for the late reply - it seems to have really been reduced since I reset the ECU. It only does it after a long trip (30 mins+ driving).

As for the revving thing it stays high when it's in neutral (takes longer to drop down to idle) as opposed if I have the clutch pressed in.

It's been driving fine anyway though.

 

Yes, that is exactly like mine. After a good run on the highway, the hanging revs issue is more prevalent. It seems to be more of a problem during the hot summer months, and less so in the winter. Mind you there were times when I was stuck in just inching stop and go traffic for an hour or so during the winter, and the hanging revs problem would start.

And like you, I also notice the revs hang high if I coast to a stop in neutral with the clutch out. As soon as the car actually stops, the revs immediately drop to 800 or so (normal idle).

 

^^^ Exactly what mine does - anoying as hell and makes it hard to be smooth at drive through speeds.

It's not a vacuum leak, the idle would stay high, not drop to normal when the speedo hits 0 - which is odd in itself.
If the speedo needle is barely off the peg, the idle hangs, as soon as it drops to 0, the idle drops to normal.

It's almost as if the ecm is trying to compensate for something but I will be buggered if I can figure it out. Maybe something with the AC compensation - cars with carbs would compensate for the extra load of the ac compressor with a little dashpot cracking the throttle a bit. Maybe the ecm is doing the same thing, just electronically?

 

Mine has done that since new, long before I added bolt-ons and tune.