I recently picked up a 2005 997 with 78k miles. A few weeks after buying, I got a few misfire codes. With unknown plug and coil age, I replaced all 6 spark plugs and coils. Cleared codes and the car has been running great... but few weeks and about 200 miles later, I cranked the car and immediately got:
P0300
P0301
P0305
P0306

Cleaned the MAF, no smoke (so likely not the AOS). Seems to be running well dispute the codes (no noticeable RPM drops, no rough idle)
Car is stock, air filter recently changed (oem).

Recommendations on what to look for next?

 

Misfires on both banks means you have to look at something common to both, like the MAF you already cleaned. Other potential issues would be a vacuum leak or a crankshaft position sensor.

Also, did you use Bosch or Beru coils or some other ones off Amazon. The cheap non-OEM ones never work.

 

OEM coils from pelican parts.

Thanks, will do some testing on MAF, vacuum leak and crankshaft position sensor as next steps.

 

Crank sensor.

 

don't rule out bad or old gas.

 

The car did sit a lot before I bought it, but I’ve been through at least a few tanks since then.

i just put in some Techron to see if maybe the injectors need some cleaning.