I have a 2011 Chevy HHR when I start it up and turn on the heat all the way I have no issues, I can let the car idle for over a hour, when I turn off the heat in about 20 minutes the idle gets slightly rough but no stalling the car runs around 160 to 170 in this condition. If I start and run the car with no heat within about 20 minutes I will get a very rough idle and the car will stall, the temperature range is usually around 180 when this happens and it has the dreaded P300 code any help is appreciated

 

to the forums!

Yep, if you're only getting 160-170 degrees, you have a failed thermostat. Use only ACDelco part number 131-158

 

And change the Dexcool while you’re at it, a simple drain and refill with 50/50 Dexcool and potable water, you can buy it premixed, and burp the coolant system to get all the air out

https://www.chevyhhr.net/forums/how-...l-p0128-24493/

https://www.chevyhhr.net/forums/how-...-system-60614/

 

In addition to cleaning the throttle body and MAF sensor, I would throw a bottle of fuel injector cleaner in the tank.

 

It’s a 2 month old thread. One time poster never came back.

 

And we offered such good advise!

 

This wasn't my post but I got a lot of good information out of it. Thank you.

 

I put in seafoam it ran much better and stopped stalling but still a little rough thanks

 

Then you still need to drain and fill the Dexcool and change the thermostat as suggested in post #2. I also recommend you clean the throttle body and MAF sensor as suggested in post #4

 

^^This^^

(Maybe a 2nd opinion will help convince.)