High idle... Sometimes.

[TIE_Fightertk06]

Hey everyone...
The little red pickup (87 R1500/305/NPA833) is acting odd:
Fires right up and idles great at 800 rpm. Warms up, all is good most days. *Sometimes* the idle (clutch in or in neutral) kicks up to 1100 and just stays there.

I'm thinking TPS? Before I start trying to remember how to test a TPS, any suggestions on where else to consider looking? IAC maybe? Where would you start?

 

[Honky Kong jr]

@1987 GMC Jimmy or @Cuba would be my logical choice for this one.

 

[1987 GMC Jimmy]

Hmm, make sure that if the clip on the IACV connector is broken that the male side is plugged in correctly. It can do exactly what yours is doing if it's plugged in sideways. Also try an IACV reset. To do it, jump pins A and B (the two on the top right hand corner) on the ALDL, turn the key to ON like you're flashing codes, wait thirty seconds, unplug the IACV connector, turn the key off, undo your jumper, and reconnect the valve connector. IAC valves can definitely go bad, and their pintles and the idle air passages on the TBI can get choked with carbon. That maybe worth checking later, but you'll have to pull the valve and the TBI unit. I'd also check for vacuum leaks. That kind of an increase in idle would make me want to check the base gasket, brake booster, or see if there's an open port. It never hurts to go through and check up on the vacuum situation. Luckily it's a TBI so it won't take long.

 

[TIE_Fightertk06]

Thanks for the tags @Honky Kong jr .

@1987 GMC Jimmy, thanks for the info. Already checked for vacuum leaks, that was my first stop. Since I'm thinking of modding the TBI, maybe I'll just pull it and go through everything. I'll try an IAC Valve reset though. I forgot which pinstopjump so that's really helpful. She's pretty clean burning, even at 251k, but that IAC valve has 46k or so on it. Thanks again!
I'll keep everyone posted.

 

[1987 GMC Jimmy]

Sounds good. I don’t think there are any other sensors to watch out for unless you have low or high TPS voltage at idle, but that’s more pertinent to idle mixture not speed.

 

[Honky Kong jr]

Thanks for the tags @Honky Kong jr .

@1987 GMC Jimmy, thanks for the info. Already checked for vacuum leaks, that was my first stop. Since I'm thinking of modding the TBI, maybe I'll just pull it and go through everything. I'll try an IAC Valve reset though. I forgot which pinstopjump so that's really helpful. She's pretty clean burning, even at 251k, but that IAC valve has 46k or so on it. Thanks again!
I'll keep everyone posted.

No problem glad you got useful info.

 

[Snoots]

I'll keep everyone posted.

That's the spirit!

 

[TIE_Fightertk06]

Finally got around to checking this issue out. IACV had a serious case of black lung. Actually wasn't too bad, but cleaned it up and did the reset and things are back to normal.
Thanks again everyone!

 

[Snoots]

Another happy GMSB member!

Woo hoo!

You must be registered for see images attach