Have Volkswagen Questions? Ask an Expert Now.
yes, the dreaded catalyst efficiency codes. How many miles on the car?
My apologies - fuel system lean...
Have you smoked the intake to look for vacuum leaks? Have you checked fuel pressure?
In a nutshell, the computer is having to tweak the air fuel mixture - adding fule - to compensate for a perceived lean condition. Low fuel pressure and volume can cause this. Extra air via a leaky intake can also cause this. Extra air entering the exhaust close to the upper oxygen sensors can set this code as well. I would be doing some smoke testing in the intake and exhaust before i threw any more parts at it.
If you put a new MAF in it, you can cross that off the list. A used part... adds another varaible. The AIR pump is only for cold start emissions. If it ran all the time though, it would mess up the signals from the o2 sensors, and could cause these codes...
Vacuum Hose Connected 51psi, engine running
Vacuum Hose Disconnected 58 psi, engine running
Residual Pressure (after 10 minutes) 29 psi