Pop On Cold Start
 

Having kind of an odd problem with my 2011 HHR 2.2L. Intermittently on cold starts I will get a single loud pop/clunk about 3-5 seconds after the engine starts. It does not sound like the typical metallic ping that you get from knocking or pre-ignition, I'd compare it more to the kind of pop you'd get from a baloon. Normally the idle speed will drop slightly prior to the pop and then jump slightly afterwords. It will not happen again on future starts later in the day and the car otherwise seems to be running perfectly.

I have watched under the hood while someone else started the car. It never happens while I am watching though. I have an appointment with the dealer for this coming Tuesday, I expect they will not be able to duplicate the problem either however and it will be a waste of time.

Has anyone else run into this and have any ideas what the cause might be?

Just a guess here, but maybe the starter is getting hung up and not disengaging after the engine starts, the drag of the starter motor would explain the rpm drop. If it only does it when the engine is dead cold, have the dealer give you a loaner so it can sit in the shop overnight, then they should be able to duplicate the problem.

Just guessing, but maybe some intermittant blockage in the exhuast somewhere. The 'pop' may be what you hear when it clears, maybe!!!!!!

EGR valve

I suspected the EGR valve as well. But it seems like the 2010/11 doesn't have one, or it's well hidden. I have a subscription to Alldata and it's not listed, nor can I find a part number for one online (i.e. on Gmpartsdirect.com).

Thought I would post an update even if it's not so helpful. The dealer had my HHR for most of the week. As expected they were neither able to duplicate the "pop" or locate any potential cause. They checked the ECM for any logged misfires and there were none as well as checking for any other possible performance issues. Also put a data logger on it to capture what was going on at a cold start and drove it around for a little while while it was warming up. Did a visual inspecting to check for anything that might be rubbing/grinding. Everything looks perfectly fine.
Of course it popped again the morning AFTER I picked it up from the dealer. :wtf:

So I guess I'm just going to have to live with the noise until it become more consistent or starts actually causing a problem. With the luck I've been having with cars lately it will be something that results in catastrophic engine failure.....just after the power train warranty expires.

It wasn't entirely a wasted visit though. They replaced my steering column to fix a rattle that was coming from it.

Holy Crap....Are they still having problems with the steering column ??

I have a 2011 1 LT.

I just developed a intermitent light rattle from under the dash on the drivers side and tried to find something loose or what ever, but could find nothing.

Did you tell them, or did they just hear it when driving/testing your rig ??

By the way.... laughed a bit about your comment,

"Of course it popped again the morning AFTER I picked it up from the dealer".


Been there done that OOOh so many times.

I had to push them on it. I had been in a week earlier and they just lubed the intermediate steering shaft, at that point it was a very obvious clunk. I was not satisfied with that as a solution. Not to mention the clunk was still there, just not as loud. I had been down the same road with my 2008 Malibu, lubrication would fix the clunk for about a month and it would be back.

It's annoying that GM still hasn't worked out the bugs with their electric power steering.