I've had a lot of trouble of late with my 2009 Chevrolet HHR.

Status:
It's firing the P0171 code all the time, P0300 sometimes, and the traction control light once.
Symptoms: Vehicle runs rough, shakes, difficult starts sometimes, often lacks acceleration with gas pedal floored. Light black smoke comes out of the exhaust.

Previous attempts:
Previously, there were other codes which were cleared by replacing O2 sensors and the catalytic converter.
We just have two smoke tests run to check for a vacuum leak. There was no leak.
The garage claims they ran tests to confirm there's no issue with: fuel pressure regulator, fuel pump, clogged fuel filter, powertrain control module, and injectors.

The spark plugs are carbon fouled and need to be replaced. I intend to do that this weekend, but am not very hopeful this will resolve the issue. I'll also check the MAF sensor again.

Is it actually likely that just old spark plugs would cause all of the above symptoms?
Any recommended next steps?

Thanks

 

It may be the old spark plugs are incorrect, make sure to install AC Delco 41-103 Iridium spark plugs.

https://www.obd-codes.com/p0171

As this information indicates, the possible cause could be the flex pipe has failed.

 

Thank you for your insight. I'm not seeing flex pipe mentioned on the provided link. Is it perhaps under another name? Thx

 

I would suspect the EVAP purge valve (the one under hood).

The traction is a result of the other stuff. Plugs should be replaced at 100,000 miles with ONLY AC Delco 41-103.

 

Thank you for the suggestions. Actually, the vehicle has only 70k miles and all of these issues.

 

Has anybody thought they were in the last century and replaced the plugs already with the wrong ones? Don't try to gap the plugs, they are gapped in the box.

 

Under Causes, it says possible exhaust leak between engine and first O2 sensor



Like this photo.