wmd13

Here is my saga for my '99 Max SE 5spd. Sorry it's long...but I figured the more info the better. My service engine soon light came on right after I moved to MD from DE and MD requires emissions testing. I checked the codes and it was 0903 - Evap Canister vent control valve. I took it to a shop and they cleaned up the valve/wiring and said the valve was still working. The light came back after a week so I took it back. They checked the codes and the evap valve came back along with the rear O2 sensor. They cleared the codes and the light stayed off and I passed the emissions test a week or so later. The day after I passed the test the light came back on for the O2 sensor. The car was running fine so I decided to put off fixing anything.

Fast forward 3 months. I took my car in to another shop to get a 90K mile tune up. They replaced the plugs with non platinum Bosch plugs (even though the guy told me they would be platinum). I picked up the car after they closed and immediately noticed that the car was misfiring under heavy acceleration and the light was blinking. I checked the codes and I got 0608 - cylinder 1 misfire, 0510 - rear O2, 0707 - rear heated O2. I took it back the next day and they told me it was a bad spark plug. The tech said he hated Bosch plugs and recommended Autolite plugs even though they didn't have any at the time. They replaced the 1 plug and the misfiring significantly improved but did not go away. I would occasionally get the light blinking and get the 0608 and 0510 codes. Once I got an 0606 - Cylinder 3 misfire. I took it back later that week and they replaced all 6 plugs with Autolite platinums. That seemed to slightly improve the situation more but still not 100%. Since the 0510 O2 sensor code was still coming up, I decided to have them replace the sensor to eliminate that variable. They have replaced the rear O2 twice and the 0510 code keeps coming back. I haven't got the cylinder misfire codes even though it does misfire occasionally under heavy acceleration (mostly in 2nd gear) and the light will blink. I'm not sure if the misfiring and O2 sensor are 2 separate issues but from reading some of the other posts, it sounds like the misfiring could be a coil pack problem.

Is it possible that a bad plug could cause an ongoing problem like this? What else could give the 0510 code even though the O2 sensor has been replaced? Is there any long term engine damage from either problem? It drives fine most of the time. I always use premium gas and I had the fuel filter replaced when they replaced the O2 sensor the 2nd time. Thanks in advance for any help.