High idle will not kick down

[anthony303]

hi got a problem when i start my 95 s10 2.2 stick at idle it gradually goes to a high idle and stays there. while driving its noticably higher and at the lights. could i have a throttle position sensor sticking or idle air control mod bad. i have a check engine light which i cannot scan it keeps coming up fault,i was told i have obd II BUT obdI? mid year change? it doesnt miss runs fine other wise.

[Chris Stewart]

Sounds like the idle air control valve is sticking. You might remove it and wipe it clean with a rag wet with carburetor cleaner then wipe out the hole it's mounted in....don't spray the IAC with carb.cleaner.

[Blue Bowtie]

You can clean the IAC with spray carb cleaner if you disassemble it.

The stepper motor that controls the IAC pintle position consists of a pair of rack gears that rest against springs. The rack gears are slightly staggered in their positions. The pintle has a mating set of teeth along its length. The two rack gears are actuated outward by the solenoid coils in the motor, and returned by the springs. If the coils operate alternately, the pintle is moved in a direction depending upon which coil/rack gear is operated first. To reverse the direction, the coils are operated in the opposite order. This is what the ECM does to control the IAC pintle position, and therefore, the idle RPM.

You can move the pintle by simulating the alternate operation of the stepper coils. If you are trying to extend the pintle, pull very lightly while you move the pintle side to side. This will alternately engage and disengage the rack gears and allow the pintle to "walk" out over them. It takes about 3-4 minutes to remove a completely retracted pintle that way.



Clean everything with lint-free cloths and a mild solvent. Harsh solvents can affect the insulation of the stepper motor coils. It's generally the dirt and buildup on this worm shaft that causes sluggish IAC operation. Set the pintle aside and allow it to dry while you clean the spring. Make sure the spring is at least 110mm long (about 2¼”. If not, you can usually carefully stretch the spring to the correct length.

When the worm gear on the pintle shaft is clean and dry, apply one or two drops only of clean light oil to the pintle shaft, then work the pintle back into the rack gears of the motor by the same rocking motion. It takes a while to get the pintle back into the worm gears, but you'll get it. It is important to get the pintle fully retracted into the housing so that the pintle is not forced against the gears when reinstalling the IAC unit in the throttle body.

While the IAC is still out, clean the air passages in the throttle body. The orifice in the TB where the IAC resides is the seat that the IAC valve closes against, and it can accumulate a lot of carbon, dirt, and debris. The easy way to do this is with carburetor spray cleaner and a small stiff brush or cotton swabs.