Thanks to all that have replied. It is nice to know I have people out there to talk to and ask questions about our HHR's. Please let me know what the dealer tells you so I can tell them what I need done.

 

I know this is an OLD thread, but the surge problem is new to me! We have a '06 LS with auto trans. When the A/C is on, the engine surges a bit when we stop. The Tach goes from around 850 rpm down to 500 rpm momentarily, and you can hear it as well. It does this 3 or 4 times until it levels off back around 850 within 30 seconds or so. It doesn't do this when the A/C is off. Anyone have any thoughts about what the problem might be?

 

It takes HP to run the AC compressor. Most cars are set to pick up in RPM when the clutch engages on the AC compressor. This prevent stall or the loss of power driving down the road.

It is normal sitting in part to pick up in RPM when the clutch on the AC kicks in.

You may have not noticed it but most all cars do this buy using a little more fuel to make up for the load placed on the engine. It takes a lot to turn the compressor when the system us under pressure when the compressor is running.

Also many car will kick off the clutch on the AC at wide open throttle. This results in the AC blowing warm air. They kick the clutch out to give you extra HP at WOT. You may have to hold it open for 15 sec at wot before you notice. it.

 

Turns out the problem was some carbon buildup in the throttle body.
Took it to the dealer and they took care of the problem for 60 Bucks. Only has about 21,000 miles on it so I was surprised that it was carboned up so soon.
Probably because 95% of our driving is just short trips around town for
almost 5 Years now.