bought this 07 HHR with 2.4 at a donation auction with a blown apart CAT at the manifold... fixed that with a new cat (bolt in)
first drive wasnt bad started missing after was fully warmed up, also struts were clunking so installed those + sway links... drives/ rides like a cadilac now
then was the misfire code... I have checked compression, replaced plugs, then coils, at some point I got the p0017 crank/cam position, so i checked and the timing chain was loose so.. new timing set (both chains) STILL MISFIRE .. I'm down to just buying both cam sensors, crank sensor and cam vvt solenoids, im not getting any specific code related to them but im at a loss, figured I'll try to get some insight from those familiar..

runs and drives AMAZING down the road, misfire is ONLY at idle

 

What codes are you getting? Seems like you've hit most of the culprits. You could take the fuel rail off and clean it out. Might also be bad injectors(s). Sensors and solenoids aren't going to cause a misfire.

 

Do you think there is only 1 "misfire code" and we all know what you mean? Code names don't mean anything.

 

Please post the actual code. We can help you from there , stand down with the parts cannon.

 

Misfires at idle indicate it's maybe sucking a little air. Maybe through the intake.

 

https://www.obd-codes.com/p0300

Gee, they didn’t get that on their list.

 

I don't have a lot of experience with these. Sucking air through the intake gasket doesn't cause misfires on these?

 

The intake gaskets are pretty stout more an o ring. I’ve never encountered an intake gasket leak, however I have seen an intake manifold leak at the brake booster vacuum hose nipple.

 

Did it cause lean misfires at idle?

 

No , it misfired across the board .
I shaved off the broken bit and drilled and tapped for a nylon pipe nipple , it’s been a few years now and I still see that HHR here in town.