RPM's not returning to idle?

[vetteboy86]

Well took the car out, with the new plenum. I noticed that when I let of the gas, the car does not decelerate. Almost like the throttle is sticking. It also wants to stay around 1100 until I have to slow the car down with the brakes. It takes a while for the car to settle back down to 600 Rpm's after I have been driving for any length of time.

I did notice that a few times, it did return to idle like normal. I have made visual checks and know that the throttle return is resting on the idle screw. I did not mess with the idle screw on the throttle body when I did the plenum swap. I also made sure the butterflies were closing all the way.

I did this several times, to make sure each time that the trottle plates returned closed. I do know that under driving conditions the RPM's dont want to come back down.

I am leaning towards that IAC. As I understand it has a needle of sorts that pushes in and pulls out allowing more or less air behind the throttle body at idle. Could this be stuck, that it would cause the RPM's to not want to return. I tried to clean it the best I could when I had the TB off the car.

Thanks for the suggestions

Craig

 

[vetteboy86]

Well my brother thinks it is the TPS. I admit it could be, but find it hard to believe, because I didn't touch the TPS. I did however clean the TB, plenum, and the IAC. I am going to take a few more looks at it.

Any other ideas....:confused

 

[rrubel]

When you cleaned the IAC, did you reset it? Might want to try that...

FWIW, my 86 does the same thing after all the rebuild stuff. Sometimes it'll idle around 1800 and if I tap the throttle it'll drop to 1200. Then after a while it'll go to 700 where it belongs. I was told possibly sticking IAC (need my laptop back to check) or throttle body bearings - which I doubt as it's essentially a brand new unit.

[RICHR]

 

[Bob Yates]

Me Too !!!!!

hey...V.B.86....In January of this year I had a intake leak so I had to take everything off to repair it. After I got it all back together I had an idle problem.I thought all kinds of things were wrong but I only needed to get everything back in sinc.... There is a thread here in C.A.C. that takes you thur the steps needed to adjust the idle. I followed it and got my idle back to where it is suppose to be. You will need a volt meter.You will have to adjust the idle stop first them the tps next and the adjustment are very small so don't move them a lot. Just keep a clear head and go slow...Good luck ...Bob Yates

 

[vetteboy86]

Thanks guys, for the replies.

Here is my situation:

If I am at low cruising speeds RPM's at or around 1100, and let off the RPM"s do not drop. I have to use the brake to slow the engine. I engage the brake, stop the car, and it falls slowly, first to 900, and then to 600 or so.

Now if I am at a slightly higher speed, say around 1400 RPM's and let off, the car slows, and the RPM's drop like they should.

I dont think I need to reset my idle, because when I start it in the morning, once it comes out of fast idle, it settles right down.

I do notice, that if I tap the pedal, it does come out of sticking. How does one reset this IAC. I am going to slowly open the plates on the throttle body, and then let them go slowly, and see if they get hung up. In other words try to simulate a cruising condition.

I will let you all know what I find, if anything.

 

[rrubel]

Sounds like your throttle body is sticking or has bad bearings. Tapping the pedal is a good check.
[RICHR]

 

[scorp508]

The TB very well could be stuck as stated. The TPS can be the culprit, but would be more likely if the idle was sticking ~1600 and not dropping at all no matter how much playing with the pedal you do along with some weirdness while driving.