It's back. At least the engine light - haven't checked the codes again. Took the car out for a drive - took hwy for about 20 mins then went onto city streets. At first red light after stopping for about 15-20 seconds the annoying beep and engine light came back on.

Plan to check code, clear it, plug in durametric with logging and go for similar drive tomorrow. What should I be logging? MAF voltage & MAF air flow, O2 left bank & O2 right bank - anything else?

 

There is actually 10 faults that pertain to the Tank Venting system and they run under different environments. You must be referencing the P0455 in which is run at 0 RPM or when the car is shut off. This though does depend on the Turbo version as it is run this way for the 997TT yet not a 996TT in which is run at idle.

Should a gas cap not be fully secured when the car has been warmed up it would cause an intake leak. The leak is compensated for by the max allowable correction for the fuel. The car has not run the Tank Vent diagnosis yet as it has not been parked or because it is to hot and rpm's are up for the other diagnosis.

The wrong plugs can also cause an issue for misfires and rich running at idle also as other unmeterd MAF intake leaks or bad MAF.

Best ,
Scott

 

Thought I'd finish this thread and let everyone know what the problem was. Took car to dealership, the analyzed the problem and determined it was one of the MAF sensors. Had it replaced --expensive part, but covered by warranty.

Thanks Scott -- you were right.