Idle too fast

reevesjo · January 6, 2016

1999 Silverado LS, 2500, V8, 6.0L I seldom drive this truck. I just start it once in awhile to keep the battery charged. Two months ago it started and ran fine. Today, I had to jump start it with a battery pack. Without stepping on the gas, it ran at about 1500rpm. I waited about 10 minutes and it was still at 1500rpm. Long time ago, you could tap the accelerator and the idle speed would drop down to normal. I tried this and it increased to about 2000rpm and wouldn't drop down to 1200 for about 10 or 15 seconds. I then took it for a test drive of about 2 miles at 50mph. When I stopped to turn around, it was still at 1200rpm. As I returned to the house, when I let off the accelerator, it wouldn't drop down for about 10 seconds and then only to 1200rpm. Tomorrow, I will inspect the Idle Air Control Valve. The Haynes book says to check the resistance across A and B and then C and D looking for 40-80 ohms and not an open circuit. Any other things to look for if this checks out??

wrenchbender · January 7, 2016

Just pull the IAC and clean the tip and clean the port. Common issue with carbon, it just hardened from lack of use.

reevesjo · January 7, 2016

wrenchbender = Genius

Fixed it. Almost in less time than it took to type the original request. It was just a little greasy, maybe a little carbon, but it wiped off with a dry rag. 44 ohms between A & B and also C & D. Tried really hard to keep from dropping the small screws, but dropped one and recovered it with a magnet. Lucky! Also discovered a partially chewed on walnut, that some squirrel left behind. Saved me $125 replacement cost. Thanks again!