OK, guys. Did the CRC Intave Valve and turbo Cleaner. It seemed to be a better product. Didn't work. Did a can and a ½. Yup, changed the oil. Maybe try that SeaFoam stuff right in the cylinder like you did next time. I give up. Although I still haven't checked the manifold bolts. May have time on Sunday to do that.

I changed the battery although I may not have needed to. Found the problem. Someone, somehow busted the negative terminal. It was loose as a goose. Replaced it. I'm not suggesting the cause of P0300, just mentioning it.

I'll check the compression again next week. I'm kind of hoping it still may improve. Possibly. From what I've gathered, that CRC can take a week of driving as it continues to loosen deposits. Not sure if i believe that, but hoping as a lazy way to fix my problem.

Thanks guys for the discussion :)

 

BTW, in the description of the GM top end cleaner: ACDelco Top Engine Cleaner is for use with 6-cylinder and 8-cylinder carbureted engines
That confused me, so went with the CRC.

 

Are you pulling the spark plugs and pouring some into each cylinder and allowing to sit overnight? Need to get it into the rings. Even this way may take a couple treatments to get it good.

 

No I didn't do that. I should have. I'll get more aggressive on the next oil change... or if the idle gets worse. I'd like to get a bore scope up there and take a look. I'm not sure what the patway is though. Through the TB and take a look I guess.

I was unaware of the fine print of a GDI engine. This carbon build up of because of the way its designed. I don't have these problems on my other HHR in which I purchased new and have around 280k on it. I always used high quality oil, gas, and regular maintenance. (I suppose i used oils with low volatility.) I wonder if my ignorance of the pit falls of a GDI engine will be its downfall. Wish I new about an oil catch can and why that's used... or that regular cleaning of the intake was a thing. I thought that was all snake oil stuff. Lol.

 

The 2.4 is not GDI.

 

It's not? It's port injection?

 

Ah, your right:

"The 2.4 Ecotec uses a conventional sequential port fuel injection controlled by ECM"

OK, now I really do give up. Lol

 

You want to really clean the combustion chambers and valves you should drop the exhaust (cat back) and do a water and or mystery oil clean. Do you know what I'm talking about?

 

No. I've seen the walnut shell method.

 

I only mentioned the CRC stuff (and the GM kit) for their directions, as evidence that you should change the oil after anything that contaminates it with solvents. I’ve used it on a LNF (DI) but never considered it for an engine with fuel-washed valves. Suppose it could help.

The walnut shells is mostly for cleaning valves in a direct injection engine I think.

There are some dirt-cheap borescopes on the the interweb that help you see what’s going on in there.

Have you taken it for a nice long run at highway speeds yet, to maybe burn some some of those cobwebs out, in case that’s the problem?