high idle on Chevy truck

[emc428]

My son has a 2000 Chevy S10 pickup, 4.3, 4 x 4, manual. Several months ago he was driving home when suddenly the truck kicked into high idle and wouldn't go back down. He sprayed the WD40 to check for vacuum leaks, found none. He cleaned out the throttle body, ran fine for about 3 miles, gunked up again and kicked back into high idle. Changed the TBI, no change. Someone told him to remove the mass air flow sensor, start the truck, then using his fingers block the two holes in the throttle body. When he did this, the idle returned to normal. So he was told it was his idle air control valve. Does anyone out there have a link to a diagram on how to replace this valve? We ordered one this morning and it will be here this week. He's been without his truck and really needs to get it fixed as we are moving soon and it can't be driven this way. Thanks for any and all help.

[AutoDoc]

its on the side of the throtal body un plug conector and un screw when you get the new prt in you will be able to what ity looks like make sure you clean the bore with airintake cleaner or it will happen again

[emc428]

Thanks. Part came in yesterday and he installed it. Definitely helped the idle issue but didn't completely fix it. Now when he gets above 35 mph, it will kick in to high idle again, but when he hits the brakes, the idle goes down. It's like using cruise control and hitting the brakes to disengage cruise. Any suggestions?

[emc428]

Still having high idle issues with this truck. Have checked for vacuum leaks, found none. Have replaced TPI, didn't solve problem. Replaced idle air control, thought it worked, then the problem began again after driving only a few miles. Any suggestions on what to check now? When we pull off the mass air flow sensor and plug the two holes with fingers, the idle goes down where it is supposed to. We have no clue where to go with this now. Any and all suggestions would be welcome.

[retired wrench]

Temp sensor for the computer may be faulty and telling the comp. that the motor is still cold. Go to autozone web site for location. RW

[marbobj]

To make sure we're on the same page:

The idle is OK until after 35 mph, then it steps up to high idle. But when he applies the brake it drops to normal level.

What happens then - does it step back up when he continues over 35 mph and drop back down in speeds under 35?

Try this - over 35 with the idle stepped up, keep the throttle where it is and apply the brake pedal slightly enough to just switch on the brake lights. See if that drops the idle.

Then, when over 35 with the idle stepped up, don't touch the brake pedal, but let off the throttle about 1/4 inch. If that does nothing, release the throttle completely without touching the brake pedal.

[emc428]

Temp sensor is fine, in fact no codes at all show up on the computer scan.

marjbob--the high idle kicks in the minute you start the truck now. Hitting the brakes/gas, does nothing to decrease it. After changing the idle air control valve the truck ran fine for about 15 miles but then started right in again. We have no clue what is happening with it now. All we know is we turn the key and the idle zooms right up. Tapping brakes, gas, or downshifting does nothing to change the idle speed. Nothing shows up on the computer scan, no warning dash lights are on signaling any kind of problem, and we are stuck.

[marbobj]

Disconnect the wiring harness from the idle air control and see if that makes a difference. If it doesn't, I would lean toward a vacuum leak. The thing that doesn't make sense is the thirty five mph business and now the high idle all the time.

[bigguy05641]

Chances are the throttle position sensor is acting up, it either has a loss of signal output, causing the ecm zero reference for idle to be lost, or, the signal voltage is hanging high after the throttle returns, causing the ecm to think the throttle is still open. Short of agonizing over the output signal with a volt meter, I'd hang a new tps on it.