Chevy HHR Random Misfire Code and Rough Idle

[Harry]

Have 2007 HHR with Random misfire code, but if hooked to scanner while car running the misfire is racking up in cylinder#2 Spark plugs have been replaced and coils be replaced injecters have been switched.What could be wrong?

[TerryAuto]

First be sure to check for a vacuum leak.

But, this sounds like a compression problem.
The 4 cyl has problems with carbon getting on the valves.
The carbon will hold valve (s) slightly open. Usually only effects at idle. Some times it is severe enough to cause damage to the valve seat.
Do a compression check on all cylinders. You may find #2 lower than the others. This would indicate the carbon problem.
You can try to have a de-carbon service done. This has about a 50% chance of helping. Do a de-carbon service and then drive it on the highway and "Blow it out" a few times.
If this does not work, removal of the head would be next. Theses heads are not repairable, so if damage to the seats, the head would have to be replaced.
If this is the case, removal of the cylinder head would be covered under the GM 5 year, 100k miles powertrain warranty.