Hi, I have a 1999 chevy silverado 5.7 liter 2500 4x4 crewcab. My issue is when the A/C is on and I come to a stop, the engine will surge in rpm. I have to apply extra pressure on the brake to keep it stopped. This happens about every other time. When the A/C switch is turned off, the surging goes away. If the A/C is not on, no surging. When the A/C switch is on low, it happens less often. I am stumped. Anyone out there have any history with this type of situation. Thanks
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i have no history with your situation but i would start by checking the tension/condition of the v-belt that spins the ac motor.

 

You amy also try to clean your thottle body, sometimes that black crust, goo can couse a thre blade to hang and the idle air motor to want to readjust itself with a load on the engine.