My 2000 Blazer engine revs 500-750 rpm when the heater or Ac is on. The vehicle will actually try to move on me and I have to keep extra pressure on the brakes when stopped. The engine also seems to rev quite high on cold mornings.

Thoughts...

Thanks.

 

could be multiple things, i had same prob changed the coils and it quite

 

Check the idle air control valve on the throttle body. This device steadies engine RPMs as loads are applied (AC compressor, Alternator loads, etc). It sounds like it could be stuck open and causing the high revs.

There should be several threads on this topic- the search function is your friend.

Cheers.
Joe