Truck Trend Garage: 1990 Chevy 2500 Pickup Idle

American Idle

Alex Steele
Mar 24, 2011
Question: I drive a 1990 Chevy 2500 pickup that won't idle when it warms up. Otherwise, it runs great. It now has 145,000 miles. Any help would be appreciated!
Photo 2/2   |   Truck Trend Garage American Idle
Answer: Start with the basics. If you have a scan tool, or know someone who does, first check for trouble codes and then take a look at the IAC (Idle Air Control) counts. If they read high (above 40), that means the PCM is sending a command to raise the idle speed more than needed to correct a problem. The two most common issues are too much carbon buildup on the throttle plate (preventing enough air from bypassing the plate to sustain idle) or a stuck IAC valve (PCM sending the command, but the Idle Air Control valve is not responding). My advice would be to first thoroughly clean the throttle plate. It’s a simple procedure: Pull the air duct, and spray throttle body cleaner all over the throttle plate and surrounding throttle bore. Then scrub with a rag and a toothbrush, getting all the nooks and crannies, and spray it down again when finished. If there’s still a problem, it could be a stuck IAC valve, which requires a special tool, a bidirectional scanner, or an experienced tech with a digital multimeter to test. The list of possible causes doesn’t stop there. It could be a vacuum leak, mechanical engine problem, and so on.

If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.

Can't wait for help with a problem you're having with your Truck or SUV? Ask the expert we trust here at Truck Trend Garage -- visit Alex Steele at
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