I just replaced the water pump on my 2001 Blazer (4.3L V6). The engine starts and runs fine but acts like its going to stall when I turn on the A/C. after a few seconds the idle returns to normal and the engine sounds fine. Strangley enough when I turn the A/C off the engine again acts like its going to stall and then after a few seconds returns to normal idle. Im at a loss. Everything worked fine prior to changing the pump and I double checked to see if I had pinched any wires or cables but everything is clear. The pump seems to work fine and there arent any leaks. I dont know where to start looking so any help would defintaly be appreciated. Thanks.

 

Not really sure that it would be the cause of what you are experiencing but did you make sure to purge all the air out of the system after the install?

 

Sounds like the IAC valve is sticking.

 

I purged all the air. Today its all back to normal. Could the plugs or something else gotten wet and made it run that way? Ill take the wait and see approach for now and see what happens. Thanks for the replies.