99 Silverado 5.3 Idles High

I have a 99 Silverado with a 5.3. When first started the idle is fine. After driving for about 10 minutes or so, stop and put the truck in park, the idle is up to around 1100 or so. Anyone with any ideas. The truck has 110,000 miles on it.

My '99 does the exact same thing. Have you had any luck troubleshooting this problem? I think there might be a sensor or something that dictates when the idle goes up while running the A/C or defrost. Let me know if you get any responses. Thanks, mijibage.

I have a 99 Silverado with a 5.3. When first started the idle is fine. After driving for about 10 minutes or so, stop and put the truck in park, the idle is up to around 1100 or so. Anyone with any ideas. The truck has 110,000 miles on it.

I caught my 2000 doing this. Just replaced the air filter, now steady around 500 at idle. Idle may be compensating for poor air intake? Just one possibility.

Could be a Throttle Position Sensor (TPS) sticking

I have a clean K&N air filter so I don't think it is that. I have thought of the throttle position sensor, but was not sure enough to spend $40 to replace it. Anyone else have suggestions?

A brick to the gas pedal, or a bottle of goo-gone in the tank? On a more serious note, my 97 Sonoma does this too. I have replaced the TPS, idle air control, cleaned the throttle plate, replaced the vacuum tubing, and more (we are also chasing a misfire).

I have been told to check the MAF and clean the filaments because the K&N oil can coat the sensor and make it run crappy. Check for a vacuum leak too.

I would suggest looking for a vacuum leak. possibly around the intake manifold. Has any work been done recently to the truck, where a seal/gasket had to be replaced?

It does not do it all the time, sometimes I can go a day or two and it does not do it. Expecially if I do not run the AC. I have not checked for vacuum leaks, but I would think if it had a vacuum leak it would do it all the time. The motor has not been opened up at all, so no gasket changes or anything like that.

My truck has about 125,000 miles on it and I recently changed the plug wires. I used the A/C Delco plugs about 2wks ago. Since then the problem has completely gone away. Not sure how that worked, but it is now idling at normal.