2006 Chevrolet HHR • 60,000 miles

I am have a Random Misfire and this is part of my troubleshooting process.
I wish to locate, inspect, & possibly replace the following:
• spark plugs, ignition wires, coil(s)
• Incorrect ignition timing
• Vacuum leak(s)
• Low or weak fuel pressure
• Improperly functioning EGR system
• Defective Mass Air Flow Sensor
• Defective Crankshaft and/or Camshaft Sensor
• Defective Throttle Position Sensor
• Mechanical engine problems (i.E.—Low compression, leaking head gasket(s), or valve problems

The odd thing is that I did not have this issue until the day after I went to DEQ and they plugged their computer into my car or the timing could be a coincidence.
June 19, 2012.

You can stop looking engine does not ues an EGR getting code P0300? Check engine light on?

Jun 19, 2012.
Of course the check engine light is on. I have experience in mechanics (Turbines). Docfixit your grammar or should I say sentence structure has no meaning and no answers. I have a P300 code and I listed the possible symptoms, and in trouble shooting we look at the easiest items to fix first and go from there. There are no aftermarket manuals on this vehicle and that I why I am using this website.
Please talk to me as mechanic to mechanic with educated answers.

Jun 23, 2012.
P0300 is normally caused by vacuum leaks and contaminated fuel

Did you checked every possible components on your list as stated above?

You need to relax here-all were doing here is trying to help you guys out. Misfires can be caused by low compression, ignition and lean fuel condition and to tell you its not an easy thing to find-Its a different story if its a specific cylinder

You can download a manual here for a cheaper price:

Jun 23, 2012.
Sorry a pdf file I cannot carry to my vehicle and reference while working on the vehicle.
I went to a shop, got a good feeling about him, took my car there and he said “it was the coil or the head gasket and it was too new for a head gasket.” I replaced the coil and the problem is now solved.

Jun 30, 2012.
Thank you for coming back with the fix and for using 2carpros-Good Luck

Jun 30, 2012.