First off the car is a '98.5 2.8. I recently had the timing belt/water pump replaced and right after the car started misfiring. It is a intermittent misfire. It will do it in all conditions (cruising, aggressive driving, engine at running temp.), it will happen at any random time. I've noticed that if it starts misfiring if I pull over and park for about 5-10 minutes it will go away. Now the oddest part about it is that it is also throwing a code for the cat (bank 1). I just replaced the cats back in May and when it does misfire I always pull over immediately (I know that driving with a misfire for a long period of time can ruin the cats) so I don't think it would have done that already. So could a bad cat cause a misfire?
Here are the codes that came up:
P0422-Main Catalyst: Bank 1: Efficiently Below Threshold
P0300-Random/Multiple Cylinder Misfire Detected
P0301-Cylinder 1 misfire
P0306-Cylinder 6 misfire
P0303-Cylinder 3 misfire
Also I've replaced ignition wires, spark plugs, coilpack (twice now, once under warranty after the first replacement one went bad within a month), both Cat. Converters, and fuel injectors; all within about 9 months. My mechanic also checked the MAF and its fine.
Could a bad cat cause this? Or possibly the rear o2 sensor be malfunctioning and be causing the car to adjust and be making it run bad? Or could it just be another bad coilpack?