My v6 did this last year too, but I didnt much care. Well now I am trying to sell this car because I have the '86, but before I sell it I want to fix this problem.

Basically, when I start the engine in the cold, it will jump way up to like 1500 RPM and then a half second later it will drop to like 500 (and often stall unless I give it gas) and then shoot back up to 1500 RPM again, and it will keep doing this until it eventually levels off after a minute or so. What the heck could this be?

 

its a fairly common problem alot of us have had, and we've yet to solve the problem

 

My surging on cold start finally went away...after replacing every sensor, fixing a vacuum leak, cleaning the throttle body, cleaning the injectors, replacing the fuel filter, removing and reinstalling the eprom in the ecm, rebuilding distributor and replacing spark plugs and wires, cap and rotor, blocking off the egr at the plenum, if i think of anything else I'll add it on.

I think it is a combination of problems as any 1 thing didn't completely cure it.
It has been running fine since middle of December, so it has seen cold and warm weather (it's 70*F outside right now).

 

I have just found out that if i take off the intake up to the throttle boddy and remove the hose then spray carb cleaner in the throttle body and clean with a tooth brush on the inside and around then to start the motor and spray some carb cleaner around the throttle body while some one feathers the throttle it can help and even eliminate the problem.
I will add to this after i try it on my car which might not be for a while since i live in michigan and its around 5 degrees out. but if any of you are having the same problem and try this reply your results thank you.

 

I'll give it a shot...

 

Mine did the same thing for a while. I replaced the MAF and it never did it again. Just a suggestion

 

Man, I'm surprised you guys haven't figured this out yet...

A lot of GM cars with the 2.8 suffer from this, but a few of the other car clubs have solved the problem.

The problem stems completely from a dirty / corroded IAC (Idle Air Control) passage. However, if any of your primary sensors are bad, it can accentuate the problem even more. If the MAP sensor, or the Vacuum sensor... or especially, the 02 sensor... if any of those are bad, it will cause the problem to only be magnified. Those sensors don't have to be bad, but often times people will replace them with aftermarket sensors, and GM electronics don't work well with many aftermarket pieces. All of your sensors should be BOSCH, or original DELCO.


To solve the problem, remove the IAC. Clean the hell out of it.. and then spray the hell out of the IAC chamber (the hole that the IAC goes into). Use a pipe cleaner, whatever.

The problem should go away.. basically, the recirculated exhaust gas from the EGR valve... coats the IAC and other components with soot.

The soot then builds up on the IAC pintle / chamber.

What happens is, when the computer is trying to aquire the proper idle, the pintle on the IAC hits the wall of the IAC hole... this hole is corroded in soot and therefore hits it sooner... it then immediately causes the computer to retract the IAC so as not to stall out. The computer... then sensing that it's idle is too high, attempts to adjust the idle down... it then hits the soot buildup on the IAC hole, and starts the process all over again... so what you end up with is a constant up and down of the idle from 500-1500 RPMs.



Hope that helps...

 

what would u recomend cleaning all that with