Question about 2004 Chevrolet Silverado 2500HD
It sounds like the computer is compensating the idle when the a/c compressor cycles on. The compressor cycles on and off when the a/c is on, which is normal. When the compressor kicks on, it puts an additional load on the engine, which in turn lowers the idle, especially at idle sitting at, say, a red light. Having the brakes on also adds another load to the engine as it uses a lot of engine vacuum to keep the brakes applied. When the engine surges, like your describing, that is the trucks computer sensing the additional load put on the engine, and is adjusting the idle higher to compensate for it. Theres really not a lot you can do about it, unless maybe switch off the a/c at red lights. I should add that if it's a severe "lunge" or surge, enough that your fighting to keep the truck from moving, I would check for maybe a vacuum leak, or even possibly take the truck to a dealer and have it checked over. Hope this helps.
Posted on Jul 01, 2009
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Posted on Jan 02, 2017
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