Setting IAC (Idle air control) valve

[Moonkilla1]

I also found this... Sounds like my situation quite a bit doesn't it

[85_Ciera_Rebuild]

Turn over, no problems idles slightly higher than normal as expected at 1000-1100
when coming back down to settle drops to about 500 and tries to catch it self

There can be no vacuum leaks...all vacuum hoses must be good, and brake-booster must not be sucking air.

So,

1. Check for Vacuum leaks
2. Check Throttle Valve's position...it must be at OEM specs. If adjustment plug is sealed, then nobody has touched this adjustment, if this is the case.

The past several older-vehicles I have acquired, I have replaced the fuel-injector's o-rings, along with intake gasket(s), and checked vacuum hoses.

What you have described is a "hunting process," whereby ECM has sent the correct "signal" to IAC, but some other issue is affecting the result.

Any EFI motor when cold will have a higher cold idle, and then it will settle down as engine warms up.

Has anyone messed with throttle plate's adjustment?

[Skip]

Have you changed the coolant temp sensor? If so, did you use a good quality one? My 3300 prefers AC/Delco coolant temp sensors. Makes a big difference on a cold start. When I was at Buick 24 years ago I remember that after market sensors would drive Buicks crazy. Also a bad TPS sensor can/will cause the computer to "hunt" for an idle as it may not be getting the reading it desires. If you tap it while the engine is idling and the idle changes, it's bad.

[85_Ciera_Rebuild]

...after market sensors...

Name branded ones, like Borg Warner or Bosch, I would not be concerned. Of course, many of those sensors are made in China these days, and maybe at the same plant that uses different labels.

I believe quality has changed since earlier days.

When I get an used vehicle, its a given, the coolant temp sensor and oil pressure sensor gets changed on a GM vehicle. I've changed out the TPS also, on one 250k mile vehicle. I believe on GMs, when coolant sensor goes bad, here comes a flooded engine, since it goes on the cold side.

A scan tool would be nice, but I've sooner or later, found the issue. I assume the MAF signal would be skewed if defective, but still working.

Needless to say, when something new/different is installed, I'd do a battery reset.

I have no idea what would happen if a reset was done with transmission in first gear, with vehicle wheels blocked, and emergency brake set. It works fine for my 2.8 engine.

[Century7667]

I've purchased very few sensors over the years, but Borg Warner is pretty solid. I bought a Standard for my '96, but not enough miles on it yet to make a good evaluation.

Ken T.

[Moonkilla1]

The Saga continues here on post #14...

http://www.a-body.net/forums/showthr...one-on-my-3300