Hello, i have mini cooper r50, 2003, 116hp. The problem is that CEL is appearing every few days with the same p0420 code (Cat. efficiency bellow and uncorrect signal). I take a car to test the emissions and everything was perfectly okay so i assume that cat. is okay. O2 sensors readings: pre-cat: oscilating between 0,1-0,9v, post cat.: oscilating between 0,75-0,9v. Is there a possible problem with timing of the engine?
Thanks for your help.

 

Here in AZ emissions testing is strictly by the OBD port. Would have never passed here.

 

Going to move you to the Gen1 Stock Problems/Issues section.