Replaced catalytic converter (old one badly clogged), all 6 plugs (with new Bosch Platinum +4s), all 6 plug wires (new Bosch premium), coil for cylinder 2, fuel injector for cylinder 2 and now the oxygen sensor before the converter. Oh, and also the air filter and fuel filter just for grins.
The only apparent things still left to replace are the mass air flow sensor and the o2 sensor after the converter. My mechanic believes it's the air sensor.
As far as symptoms go, the car was running fine before but now sporadically starts sputtering and missing a bit at idle (usually when it's first started or I'm stopped at an intersection). It actually seems like it might be a bit WORSE since we changed the upstream o2 sensor this afternoon.
Just replaced the mass air flow sensor and it seems like it might be running slightly better, but the check engine light still flashes periodically and the engine still runs rough periodically. Could it be the sensor relay?