Fast idle when stopping

[homes4you]

My 2000 Sierra 5.7 has developed a minor problem. When starting the motor, warm or cold it jumps up to around 1500 rpm then adjusts down to around 850 rpm. While this isn't so bad, the more annoying problem occurs when slowing down in traffic. The motor seems to have a cruise-control mode holding it around 1500 rpm with my foot off the gas. (As in slowing to a stop sign) It continues to idle high until either stopped or almost stopped then comes down to 850. This problem comes and goes with no apparent reasons. There are no codes showing on the dash. The problem is worse when the AC is on and makes the truck difficult to stop.

This High idle problem does not happen when the truck is in park and you hold the motor around 1500. As soon as you release the gas, the idle comes back to 850. I have checked the vacumn at the brake booster and have 21 inches at idle and the motor runs great.

Any ideas please.

 

[happy 2011]

sounds like a IAC (idle air control) motor. Check that frist maybe clean it but most of the time there just bad.

 

[homes4you]

Thanks for the Ideas. Today, the weather is cool enough to get out and work on the truck.

I started with removing and cleaning the IAC. It was not too dirty nor was the throttle body dirty. I replaced the IAC with a new one and the driveablility problems are solved. It does still idle up a bit when I first start the motor (warm or cold), but I can live with that.

Thanks for you help.

 

[happy 2011]

your welcome