Hey All,

Been having a weird problem with my 97 z28 m6... For the past couple of months what has been happening is when I am driving and want to switch gears I press the clutch and the engine does not rev down, but revs up until I put it in the next gear or punch the gas down a little and then it falls slowly down to around 1.2k rpms. Same thing happens if i put it in neutral such as when i stop at a light i have to tap the gas to make it fall. It feels sort of like the accelerator linkage cable is getting stuck but i checked it and its fine :-(

I have tried revving the engine under the hood and it looks like the link stops right before it falls against the screw so the engine still revs a bit higher until i push the link down. With the engine off, this doesnt happen at all, the link just falls against the screw without a problem, only when the car is on it does not fall totally, but there is no tension on the link cables that go to the pedal. Sorry for the long description, just wanted to give as much detail as i can :-)

Thanks in advance for your help everyone!

Wally

 

btw, i should mention, the car is supercharged, not sure if that makes a dfference with the problem though....

 

Try lubing the throttle return spring and butterfly rod with some WD40. Also, it could be an issue with your IAC (Idle Air Control, that little motor underneath the throttle body) or TPS (throttle position sensor, that little black sensor on the side of the TB).

 

Thanks, tried lubing the spring etc. seemed to help for a minute, but problem came right back :-(

Its weird because there are times when its normal, but thats happening less and less...

Any easy to diagnose if its the TPS or IAC? Its weird because the butterfly seems to come go back perfectly, yet when the car is on and i move it it falls back just short of hitting the little screw until i move it back down myself, there doesnt seem to be any pressure on it, it just kinda stops right before hitting the screw. I went to the dealer, but they wanted $140 just to check what it is! and when i went to a couple mechanics they didnt even want to listen to what i was telling them and just told me to leave my car overnight and they will take care of it.... grrr, i hate dealing with mechanics!

 

I'd remove and clean the TB & IAC passages & pintle (careful not to change the position) if that hasn't been done...

 

I've seen that problem on an LT1 w/ an aftermarket TB. I believe the solution was to shave the butterflies down since they were binding up on the housing.

 

Thanks for the suggestion, but already done the cleaning :-(

The tb is stock and seems to close up fine when the engine is off... only when it is on it does not close totally by itself until i press it closed...

It's getting to be really frustrating when driving and everytime i press the clutch the engine revs up all way to 2 or 3 k rpm....

thanks again all.. i appreciate all suggestions :-)

 

scan it and see what it is doing. If you do not have a scan tool autozone does free scans I think. Sounds like IAC to me. My moms 94 z28 does something similar, when stopped it will rev up sparatically and try to jump forward if not in neutral. Also I guess it could have something to do with your program on the car, since you have a supercharger.

 

thanks, how does the IAC actually work? does it somehow force the tb to open more? thats what it seems like is happening since when this happens and i come around to the engine i can push the butterfly closed with my hand....

Thanks again!