starts unning rough when I warn it up. turn off, restart and runs fine
 

My 2010 Chevy HHR just started doing this 3 weeks ago. It started happening when it was -20 below zero, and now it does it randomly. It always does I now when I am warming it up. I can turn it off and start it back up and it runs fine. I tried getting the codes ran today but there system was down so I am going to try again tomorrow. I just thought I would come on here to see if anyone else is having this problem. Totally frustrated

Get the codes and we’ll go from there.
it could be many things!

So many possibilities. Been running with a CEL? Any other issues, current or recent?

It seems virtually anything amiss in your emission system can cause trouble with your FlexFuel system. These problems also seem to be associated with the onset of cold weather. I’m not yet saying this is what’s going on, but when you scan for codes, do also check the stored ethanol %. The importance of this might be ignored or poopoo’ed by others, but it’s been the underlying cause of several mysterious cases, here and other GM FlexFuel cars (not just HHR.) The ethanol %, not being an error code, is often buried in the menu structure, but is always available on a robust scan tool, and often even in the most basic code reader.

Looking forward to seeing the results of your scan.

Ever run E85? (Not a bad thing. It’s great stuff, just helpful to know.) Do you ever smell gas outside the car, or have you seen any other evidence of a fuel or a vape line leak? Does the car make a lot of short trips?

Maybe premature, but I’m here whacking away at the keyboard so:

Sometimes the problem is corrected when the ECM detects a normal refueling event. Hot car, engine off, adding more than about 3 gallons, driven away still hot, results in a stored ethanol % adjustment. Get high-quality regular (“TopTier” brands: Sunoco, Exxon Mobile, Shell, etc., any major brand but BP. No bargain brands.) High-octane not recommended.

Cleaning the MAF sensor is always a good idea. Quick and easy.

And clean the throttle body correctly too. Use quality spray formulations to gently clean both.