2007 2.2 AT 159k Sorry to beat a dead horse, I apologize for my lack of forum etiquette, I read a lot, but never post. Redirect as needed.
Totally frustrated with an idle surge issue, rough idle, runs perfect off idle, poor fuel economy, P0300 code, replaced damn near everything, I work at Oriellys and get a nice discount. I am tired of throwing parts at this problem. HELP! My 2006 2.2 manual runs perfect at 180K

I'll list new and tested parts.
New AC plugs, 4 new injectors (today), new purge solenoid, tried and returned 4 coils (no change) , alternator tested ok at 13.6 volts, swapped MAF from known good 2006 2.2, tried Techron, Lucas, compression 150 +/- 3 psi, tc light was on before injector replacement, but would clear if I restarted it, now tc light is staying on, I have a innova 5210 scanner, doesn't tell me everything, but should help.
I was thinking fuel, since I had replaced ignition parts, injectors, maybe a smidgen better, but still not right.
I find it hard to old school test for vacuum leaks, carb clean,
ether, because i have to remove air cleaner to get there and that involves removing MAF as part of air cleaner assy.
It is a good solid well optioned car, with all new hard parts, I want to keep it.

Any more ideas, I think I have read every forum on this problem, only thing I haven't done is check for proper ground at BCM, ECM.
Also could still be a vacuum issue, considering the T/C light.....????

Thanks in advance, I love my HHRs!

 

Have you cleaned the MAF sensor and the throttle body? With proper cleaning spray for each , not carb cleaner! That will damage both.
AC plugs? 41-103 Iridium AC Delco plugs?
have you removed the valve cover inspected the timing chain and the front timing chain guide?
I had a 2007 2.2 , sold it at 386,000 miles , so I’m not new to these symptoms.
have you tested the fuel pump, if so what was the pressure?

We are here to help you find the problem and learn how to fix it!

 

Throttle body removed today new gasket, and cleaned with CRC, just prior to replacing injectors! MAF was swapped with a known good from my 2006 2.2. no change. Forget which plugs I put in, Orielly computer told me which ones. As for timing chain, haven't even considered that yet.
Also haven't tested fuel pump pressure, figured since it runs perfect just off idle, it can't be fuel pressure, I was thinking fuel delivery, injectors?

 

While the T/C light is on use a scanner that reads ABS codes. Or, does the T/C light only come on when the P0300 is set? If that is the case the P0300 is the cause of the T/C.

Water in oil, oil in water, borrow a exhaust gas kit. Disappearing coolant? Oil level increasing.

Unplug the ECM inspect all the contacts, apply dielectric grease.

Test fuel pressure, clean TB. Tighten clamps on intake tube. Inspect tube for cracks (especially at the PCV entry).

 

Fuel pressure is the basis of fuel delivery, I installed new injectors in mine and there was no improvement, those spark plugs may be incorrect, lotsa parts palaces recommend incorrect plugs. Oh, they fit but do not function as designed.
a Known good MAF is not a clean MAF , same with the throttle body , did you spray it with throttle body cleaner?
as Jack Webb stated on Dragnet, just the facts please.

 

X2 with Oldblue's reply.
CRC makes many products that are not interchangeable.
I have CRC brake cleaner, MAF cleaner and Throttle body cleaner
Which was used?
The spark plug brand and temp range does make a big difference.
Ask me how I know.
Check for vacumn leak.

 

MAF I still question!

 

Thinking evap/fuel delivery now! Removed gas cap, condition seemed to improve.

 

Are there codes indicating EVAP? Have you tested the EVAP purge valve ? The one under the hood , if you can blow air through it , it’s failed, but it should throw a CEL code.