My 2001 911tt just started throwing a P0491 and P0492 code. I have read in previous posts that this code can be due to a vacuum leak at the Combination valve for secondary air. I checked the connection and it seems fine. The car runs fantastic, but I have noticed fuel mileage getting progressively worse. I figure that is due to the lousy 91 octane oxygenated fuel here in Aurora,CO.

The only maintenance I have done to the car in the last few months was to replace the cabin air filter with an OEM part and change the engine air filter to a K&N.

Would any one of those possibly be the culprit for the codes? If not, any other troubleshooting ideas would be greatly appreciated.

 

In your post you do not mention if you hear the air pump running...Engine compartment on the forward right side there is the air pump and this pump should start for few minutes after cold start...

 

Had to let the car cool all the way....when I started it the air pump did run for a little less than a minute.

 

The air leak we are talking about can be really minimum. Sometimes hard to hear or to feel. it can be from one of the lines on this drawing. These are sense line. May be one is disconnected. Very hard to see all of them....