Surging After Thermostat Replacement

[UMEXT]

Hi, I had a check engine light on. The associated codes said either thermostat or coolant level sensor. I was (apparently) losing coolant. Today, I had the thermostat replaced at my Chevy dealer; the light is off and stays off.

Unfortunately, the engine now surges, then dies down, then repeats the process. If I stay at idle for more than 30 seconds or so, the engine shuts off. In driving home (a distance of about 40 miles), it has now decided to do the same thing while in cruise control, though the engine does not die in those circumstances. It did not do this, not even once, before the repair.

Do I have incredibly bad luck and timing, or is there a connection between the repair and this new concern?

Thanks!

 

[barron03]

Check this out .http://gmtnation.com/f25/how-clean-4-2-inline-6-throttle-body-221/#post3362

 

[UMEXT]

Check this out .http://gmtnation.com/f25/how-clean-4-2-inline-6-throttle-body-221/#post3362

Okay, and thanks, and I may do this, but my question is, how is this related to a thermostat replacement?

 

[barron03]

If they disconnected the battery and the tb is dirty .

 

[The_Roadie]

Dirty throttle bodies usually cause erratic idle when the AC compressor cycles on and off. Forcing the compressor off is one experiment that can point to the root cause. Dirty throttle bodies usually don't affect the engine above idle, but an extraordinarily dirty one might. In 100 miles or so of driving, the PCM might relearn the throttle body's behavior because the dealer should have disconnected the battery, but if you have over 30K miles, cleaning it is just a plain good idea anyway. Then see if the behavior changes.