Super high idle

[TURBO2]

I'm having troubles with a super high idle on my 1986 GN and I can't find a cause for it. I tried resetting the IAC and with the throttle blade completely closed (idle screw backed out completely) it idles at 1,700 RPMs and then cliimbs to a little over 2,000 RPMs. At this high idle it is pulling between 15 - 17 on my vacuum gauge. The first thing I did was to check for vacuum leaks. I've tried my smoke machine going in the intake tube after taking the MAF out, and I've gone directly into a vacuum line and I can't find any leaks. There is no smoke coming out anywhere in the engine compartment, under the vehicle, or inside the vehicle. I also tried spraying brake cleaner on all vacuum connections, injectors, intake manifold, and all around the TB with no change in idle. I then tried pinching off vacuum lines and also plugging off vacuum lines and still no change. Is there something else I'm missing that would cause this?

 

[nwarky]

Went through this exact problem a few weeks back. After confirming no obvious vacuum leak just as you described I decided the IAC valve was the culprit and indeed it was.

 

[TURBO2]

Went through this exact problem a few weeks back. After confirming no obvious vacuum leak just as you described I decided the IAC valve was the culprit and indeed it was.

Was it an internal leak?
I checked all around the outside sealing area of mine.

 

[750H.P.V6]

It sounds like your TPS is set wrong. If the voltage is above .5 volts with the throttle closed you will have a high idle.

Neal

 

[TURBO2]

It sounds like your TPS is set wrong. If the voltage is above .5 volts with the throttle closed you will have a high idle.

Neal

TPS is brand new and set to spec.

 

[Mr.Spool]

Replace the iac.
When they go sounds just like your problem

 

[dynoman]

The IAC is a motor controlled valve . It isn't on or off , it varies it's position to control idle , so a 35 year old motor controlled valve going bad isn't out of the question ! lol
Cruz performance makes an adapter for using a modern LS IAC . I have one going on my car soon .

CRUZ Performance LS IAC Adapter

CRUZ Performance Turbo Buick IAC adapterConvert that old lazy IAC over to a Modern LS Style IAC that is faster,more efficient and will also eliminate the need for IAC Angle adapters CRUZ Performance LS IAC adapter includes AdapterGasketStainless mounting hardware

cruzperformance.com

 

[TURBO2]

The IAC is a motor controlled valve . It isn't on or off , it varies it's position to control idle , so a 35 year old motor controlled valve going bad isn't out of the question ! lol
Cruz performance makes an adapter for using a modern LS IAC . I have one going on my car soon .

CRUZ Performance LS IAC Adapter

CRUZ Performance Turbo Buick IAC adapterConvert that old lazy IAC over to a Modern LS Style IAC that is faster,more efficient and will also eliminate the need for IAC Angle adapters CRUZ Performance LS IAC adapter includes AdapterGasketStainless mounting hardware

cruzperformance.com

Thanks for the info.

 

[nwarky]

I never confirmed a vacuum leak. As mentioned above the 35 year old IAC valve finally failed. When it was removed it was fully extended and there was no adjusting it. This does happen to be one of the more expensive parts but lasting 35 years it's difficult to complain. Replacement was $48. I am totally confident that is your problem.

 

[TURBO2]

I never confirmed a vacuum leak. As mentioned above the 35 year old IAC valve finally failed. When it was removed it was fully extended and there was no adjusting it. This does happen to be one of the more expensive parts but lasting 35 years it's difficult to complain. Replacement was $48. I am totally confident that is your problem.

Thanks, I ordered one today and should be here tomorrow. It would be nice to finally be done with this and move on to upgrades.

 

[TURBO2]

I got the new IAC today and no matter what I do 750 - 775 RPMs is the lowest I can get it and that is with the idle screw doing almost nothing, just barely touching.

 

[TTA308]

750 - 775 RPMs

750 or 1750 ? 750 is normal

 

[TURBO2]

750, procedure is saying 500 +/_ 50

 

['87 Turbo "T"]

Mine w/60’s is 800-850. So youse doin’ fine.

 

[TURBO2]

If after mod's the old IAC reset procedure of 500 +/_ 50 is no longer relevant, what should I be using for a target?
3.5" MAF
70mm TB
60# Motrons
3" TH downpipe

 

[Chuck Leeper]

what should I be using for a target?

Whatever the engine likes, based on the mods.
BTW, with those mods you certainly don't need a 70mm t/b.
Also, where are the SM readings?
What does the SM show the IAC at, at idle?

 

[TURBO2]

Whatever the engine likes, based on the mods.
BTW, with those mods you certainly don't need a 70mm t/b.
Also, where are the SM readings?
What does the SM show the IAC at, at idle?

IAC is 35 - 37 at idle right now.
I'm still upgrading so I wanted to just switch it out to the 70 and not upgrade again.

 

['87 Turbo "T"]

IAC is high. I keep mine in the 10-20 range. Each car is different though.

Change IAC & it’ll change TPS setting & vise versa. You have to do the dance between both & get them where you want.

IAC-10-20(idle) TPS-.40-.44(KOEO) 4.1-4.4v at WOT(KOEO).

 

[TURBO2]

IAC is high. I keep mine in the 10-20 range. Each car is different though.

Change IAC & it’ll change TPS setting & vise versa. You have to do the dance between both & get them where you want.

IAC-10-20(idle) TPS-.40-.44(KOEO) 4.1-4.4v at WOT(KOEO).

Yeah, I've been going back and forth between both, but trying to get to the 500 mark was screwing it all up.

 

[750H.P.V6]

Since you're running an aftermarket chip, do you know what the programmed idle RPM is? 750 RPM doesn't sound out of the realm to me.

Neal