Engine holds on to RPMS when revved


New Member
Mar 22, 2010
Atlanta, GA
So I have a 98 GT vert with an AOD trans. I did a 2001 PI motor swap this week. Problem is when I rev the motor the RPMs SLOWLY return to idle. Not a nice crisp rev and return to idle. It revs quickly enough, just takes a few seconds to slowly drop back to idle.

I think its a tuning or ECU issue since it was this way with the 98 motor and is the same with the 01 PI motor.

Any input? Thanks

Is there any visual way to inspect the difference for 98 2V and 01-04 PI 2V?
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The slow return to idle is for smog reasons. They all do it.

If the idle hangs for excessive periods, 1st check the throttle body linkage. Ensure it moves freely. Check the throttle return spring.

Did you alter the throttle body set screw? This could be allowing too much air to enter. This will cause a high idle.

Next check for vacuum leaks.

Finally, suspect a bad TPS.

If it really bothers you, there is a IAC restrictor gasket on ebay.
It idles beautifully. The other motor did too.

It just bothers the heck out of me that it returns to idle from a rev so slowly.

I mean REALLY bothers me.

My GT500 revs smooth, sounds mean as hell, then quickly returns to idle.

My 98 with 01 PI motor revs smooth, sounds good, and (like grandma's car) slowly returns to idle over a few seconds.

I really want to get rid of this.

Throttle spring looks good and TPS screw seems fine too.....It wasn't altered when PI swap was done.

Dunno.....was thinking of ways to get rid of that slow return to idle.
Yah UDPs are in the very near future and I am planning to upgrade the throttle body to 75mm version next week too.

I am hoping as the mods increase this annoyance goes away.

Just looking for a magic bullet of sorts to fix it ASAP.

Yah........i just want em all to be fast as hell and sound as mean as anything out there when ya rev em.

I don't see the problem with that.:D

You are absolutely right....it doesn't make it any slower......and it moves a lot better with the 01 PI motor than it did with the stock 98 2V. Guess I shouldn't whine.

Thanks for the input all.
Yeah I can see that, it was something that was kind of annoying when I first got my car... I'd be like hey doesn't this sound good? Rev.... still revving, revving slower, back to idle. It doesn't give that satisfying throttle blip of muscle cars of yore.
Im glad Im not the only one that feels that way BlackStang03.

Dunno, and that's what I am hoping to get answers for here. :D

I would love to have that quick throttle blip and roar.

If I figure it out with the mods/bolt ons in the near future I'll let you know, I was just hoping someone has already been down this road and knew a fix.