1989 Olds Sierra surging at idle?

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Cool forum :thumbs:

My neighbor has a 1989 Olds Sierra that has 68K on the odometer and was having some problems with the motor surging at idle when warm while in gear. Engine does not stall. Then a hesitation/stumble upon acceleration.
I suggested fuel filter, plugs. He did and still same symptoms with no inprovement.
Possiability of IAC carbon build up? If so is it that difficult to maintain? Dissassemble and clean out the carbon....right?

Any other suggestions/comments would be really appreciated.

This seems to be a very informative site/forum, I like it! :laughing:

Thanks in advance for ALL help!

Tom McBride
Long Beach, Ca.

posted by  tommcbride

Use an ohmeter to check the resistance of the Throttle Position Sensor. There should be 3 wires going into it. The center and one side should build up slowly and evenly as the pedal is slowly pressed, and the center and opposite wire should show a reverse but steady reading. If there are jumps in the resistance it is junkola.

That's what i would check first.

Of course it could be a lot of other things such that you already mentioned. Does it seem like it's running rich? Could be a coolant temp sensor, if you want to test that give a holla.

Is it a GMC Sierra or an Olds Cutlass Ciera (just kidding)

posted by  carls47807

It's a Olds Cutlass Ciera, :screwy:
Thanks for the tip on checking the TPS. I'll do that. BUT just in case it is not that and I need to search further, how can I check the coolant temp sensor?
AND also when I am cleaning the IAC is there any (re-adjustment) I'll need to do OR just screw back on with no adjustments....THANKS again for your assistance!


posted by  tommcbride

just screw it back in, but make sure that the distance from the seating surface to the end of the pintle is less than 1-1/8". what engine does it have?

posted by  dodger65

hey dodger. i heard you could check the IAC with a 9 volt battery, you know how to do that? and whats the 1 1/8" business? thanks

take the coolant temp out and hook an ohm meter up to it. wrap your hand around the base of it and the resistance should continously change. if it's bouncy or does crazy stuff replace it.

posted by  carls47807

It is a 6 cylinder

And thanks for the tip on the IAC and the distance :thumbs:

posted by  tommcbride

THANKS, I'll try this if i need to. :thumbs:

posted by  tommcbride

you can test them w/ a 9V battery. i'd have to look at a wiring diagram to remember which terminals you hook up though. apply 9V to two of the prongs at a time and one set runs the pintle in and the other runs it out...

the 1-1/8" thing is the depth of the iac cavity and you want the pintle to be shallower than 1-1/8" to keep from bottoming out and scoring it when reassembling...

posted by  dodger65

the bottoming out is to allow the computer to know where the 0/start count is

posted by  osborste

right. what i'm saying is that you want to put it in shallow and let it bottom itself out gently, rather than jamming it in there and scarring up the pintle...

posted by  dodger65

WOW, what a GREAT forum!

Thanks to everyone for your suggestions.

I'll let you know where we stand in a few days when he gets the car back from his daughter.

posted by  tommcbride

I have finally got a chance to check his car out and after talking with him and taking it out for a ride here is the real deal.

The engine runs fine when cold and at idle, when warmed up to operating temp the vehicle will "stumble" upon load i.e acceleration....not hard acceleration, just meadiocre acceleration, normal accel, you can detect just a faint hint that it is "missing" "stumbling" but it is not pronounced. OR when going up a rather step hill it is pronounced.

1) IAC cleaned
2) Spark plugs are a bit rounded and not a lot of carbon deposit build up...I have recommended replacement
3) Wires are original (60K) I will be replacing those (I have a feeling they mak be breaking down) What is the OHM resistance of the wires? Does anyone know?
4) Dog bone mount and other mounts are sound and solid
5) Air filter new
6) Fuel filter new
7) Coil does not appear to have any cracks or deformities on the exterior

Am I missing anything?

AGAIN, thanks folks for your help!


posted by  tommcbride

bump :smoke:

posted by  tommcbride

sorry, dude. been workin' a lot... do you have any codes stored? also, check the fuel pressure. also, also i really need to know which V6 it has, the 2.8 or the 3.3... :thumbs:

posted by  dodger65

spark plug wire resistance on most cars (inc. GM's) is typically between 5000 ohms and 7500 ohms/ft.

One many of these cars, the plug wires should be replaced @ 60K miles as a preventitive maintenance procedure.

posted by  tbaxleyjr

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