Originally posted by Big Jim:
Two general comments here.

Almost always when both oxygen sensors read either rich or lean, it isn't the sensors that are faulty. Look elsewhere for the actual cause. There are other things that can cause rich readings.

Only the upstream oxygen sensors have any impact on running rich or lean. The downstream oxygen sensors only have to do with the cat monitors as I recently posted on another thread.



Yea the O2 sensors are the last things that I would think it would be. I have tried many other things though to try and fix the problem. So far I have checked the fuel pressure, replaced the MAF, cleaned the TB, replaced the PCV valve and checked for apparent vacuum leaks. Today I am throwing in a new ECT sensor, so if that doesn't fix the problem I am not sure what else to check.....

2001 Volvo S40-Perrin MBC@ 11psi, EST intake, 35% tint, still slow