Power surges

[jrealmuto1]

When driving, I cut my heat on. The engine will power surge and cut off and back on. Tested alternator and it read bad. R&r alternator. Everything running good for a week. Until now. Back to the same thing. What would be my next step?

 

[koda2000]

did you also check your battery? a bad battery can ruin an alternator pretty quickly. also have you new alternator tested. it may be defective

 

[angstrom08]

Let me guess, you live somewhere cold? I noticed the same behavior.

So, both defog settings as well as the dash+floor setting engage the AC to dehumidify the air to prevent/reduce condensation. Try selecting the dash only or floor only vents - if this stops the surging, then I'd be 99% the problem is the PCM increasing air+fuel by opening up the IAC valve further.

I noticed the same behavior beginning this winter. Initially, when I realized the surging was the AC engaging, I began to hypothesize the PCM was accelerating the engine a certain amount to offset the increased engine load from running the AC. If the AC was failing to load the engine sufficiently, then the PCM would be overcompensating. I don't know enough about the AC system to decide if that's even plausible much less how to check that.

Unfortunately, I'd also replaced my IAC valve this summer so I can't rule that out.

I guess, it'd be useful to know if your air con worked this summer?

Good Luck