My Blazer runs great except it surges a bit in idle and drive only when the heater or AC is on. Wondering which sensor/switch might be the cause?


Thanks,


Matt

 

How substantial of a surge are we talking? Probably your a/c compressor kicking on/off. Unplug your compressor and see if the "surge" goes away.

 

Thats what I'm thinking. AC compressor. They always used to do this when you used the defrost setting on the heater to keep the clutches free even in winter. It will cause a slightly noticeable stumble under normal conditions. Really just a slight decrease in engine RPM is what it is. Just a little drag.

 

If you have automatic climate control, the A/C compressor can cycle in any setting except off. If you have manual HVAC, the compressor will only cycle in A/C and defrost settings. The compressor cycles in defrost to blow dehumidified air on the windshield to defog it quicker. The PCM will compensate for variances in engine RPM as the compressor cycles on and off, and you may or may not notice it.