truck idling too high when cold?

Question

I have a '91 Chevy S10, and in the winter months it idles too high when the engine is cold and I first start it up. When I approach a stop sign, it will barely let me put it in first gear (it's a standard). What is the problem, and how do I fix it?

Answer 1

Your idle is controlled by the ECM. The ECM sends a signal to the IAC (idle air control) motor. The IAC motor has a plunger that changes the A/F (air fuel) ratio to control idle speed. There are sensors that feed info to the ECM to help it determine idle speed. The 2 main sensors are the coolant temp and manifold air temp. there mat be a problem with 1 of those.
Another common problem has to do with the IAC plunger. It can get groves wore into it and carbon can build up on it.

Answer 2

How high? It's supposed to fast idle when cold, the alternative is not running. But it should be like 30% higher than normal, not twice as fast.

It also shouldn't affect engaging a gear unless your clutch isn't releasing properly, so that the input shaft is still being driven. Do you sit with the gear box out of gear and the clutch up? If so then the engine is spinning the input shaft, so when you tread on the clutch and try to engage first you are using the synchromesh on 1st to stop that shaft so the gears can mesh. Being British I sit at stops and lights with my F250 in 1st and my foot on the clutch. If I am engaging 1st when I have been standing out of gear with the engine running I depress the clutch, select 3rd or 4th and then 1st. The synchros on the higher gears get less wear, so I am using one of them to stop the input shaft before I engage 1st. I learned to do this on an ancient Bedford TK diesel truck with a very worn (300,000 mile) drivetrain.

Depending on how the fuel system is managed it could be as simple as the fast idle being out of adjustment, on one of my old cars it was adjusted with a screw on the throttle body.

Answer 3

let it idle a few mintues before putting it in drive initially. happens with all cars.