Takes a little bit for rpm to come down

[Woody103]

I just got my 94 gt running after sitting for two years it seems like the rpm’s do not drop right down after I let off the throttle . Like when shifting the rpm’s stay up when I’m shifting kind of hard to explain but hope you know what I’m talking about .

 

[96blak54]

Oh yes....we all know EXACTLY what you are talking about! Hanging rpm and hanging idle is synonymous to sn95's

Anyhow, get your car running and go over all the vacuum hose, intake pipe, and intake gaskets. You are looking for any air being sucked in from anywhere other than through the mass air meter.

 

[ttocs]

the only time I had an issue with it was with a pro product throttle body. When I swapped to the edlebrock it went away. There is a piece you can buy that allows you to adjust the IAC vent size to restrict it but last I saw I think it was around $50.

The cheap option is to make one by guessing/playing with the size of the hole you make yourself.

 

[Woody103]

Ok thanks at least I know it’s not me thinking it wasn’t right.

 

[shovel]

Two things to look into while checking for leaks -

First is the evap solenoid. If the vac hoses on it are backward it can pull itself open with vacuum. The hose farther from the electric connector should go to the intake manifold. That might be connected under the manifold, which is difficult to troubleshoot without removing the top of the manifold.

Second is the PCV, those are not universal devices even if they look the same and they can get stuck partially open or partially closed.

I don't know for sure what's in the stock ECU but on aftermarket EFI systems there is a function that holds open the IAC valve some fixed amount whenever engine RPM is over some amount (like 1300 or 1500 etc) basically to work like a dashpot on old carburetors; prevent the engine from flooding every time you lift your foot off the gas pedal. It supplies enough air to burn off the last bit of extra (above idle) fuel while you decelerate but it's a balancing act because the hold RPM has to be low enough to not leave a huge gap where it's not doing anything and high enough that it's not the cause of a hang all by itself. If you have other sources of air (or fuel) beyond what's necessary for idle it can stay above that threshold and keep itself hanging indefinitely.
Keep in mind I'm talking about aftermarket EFI systems here and I am only inferring that the same behavior might also apply to the stock EFI system and it might be helpful while you troubleshoot your car.

 

[ttocs]

a smoke check would probably be the best way to start. More than likely you have a factory line somewhere that is cracked and letting extra air in. Do a search on youtube and/or find one of your cigar smoking friends to stop by.

 

[Woody103]

Ok will start looking when I get back home thanks