1999 Chevrolet Silverado



November, 19, 2008 AT 11:32 PM

Computer problem
1999 Chevy Silverado V8 Four Wheel Drive Automatic 265000 miles

I have changed air idle valve, cleaned thottle valve& MAF with air intake cleaner. Engine idle is still slow coming back after being revved up. Also seems to be worse when temp of air is cold. PLEASE HELP !


3 Answers



November, 20, 2008 AT 9:48 AM

If you work the throttle by hand, with the engine running, do the rpms drop quicker. Can you tell if the throttle plate, is closing, and not being held open, someway?

If you start the vehicle and let it idle, without touching the throttle, are the rpms ok?

Can you check the signal on the tps? I 'm not saying, replace the sensor.



November, 25, 2008 AT 11:22 PM

The thottle plate returns all the way. When the engine is started it idles high, sometimes at 1200, then sometimes slowly comes down to about 800. I probably could check the tps switch if you could give me some guidance. I have 30 years as a commercial tuck mechanic but not too good yet with automotive computers yet. I am very grateful of any help given!



November, 26, 2008 AT 11:29 AM

A lot of vehicles will idle high on cold start-up, then gradually go down as the engine warms up. I did see the code you listed.

On a fully warmed engine, is the idle still a problem? I'd want to see the iac counts and you need a scanner, where you can see live engine data.

If you have a scanner, it will show what the sensors are doing, or you can backprobe the dark blue wire at the throttle position and use a dmm, turn on the key, you don't have to start it, have helper work the throttle. The voltage readings should move smoothly, up and down as the throttle is moved.

Without at least a scanner, it's just hunt and peck. There are several things that might request a higher idle, if it isn't some kind wiring or mechanical issue with the iac system.

The alternator--hvac--power steering, just to name a few, may cause the computer to request a higher idle.

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