Just wanted to thank all the knowlegeable folks on this site. Bought an '02 Lancer ES for my daughter's first car. Of course, had to work out some used car issues like new tires, brakes, and fluid changes. After discovering and reading this forum, I decided to change the timing and accessory belts. When I picked up my car, the battery was dead. A quick jump got me going, and went straightaway to the auto parts store to have battery checked (and eventually replaced). While I was headed there the car was running awful - poor idle, surging, stalling. I decided that before I did anything else I'd read past forum posts. That's when I learned about the computer having to relearn, and just as was written, the smooth idle returned in about 100 miles! So when my SES light illuminated a week later I was right back here discovering the recalls that the last owner ignored. P0421 definitely means a bad cat! The dealer reprogrammed the PCM for free, but could not cover the cat (118,000 miles). I do have some advice for folks who find themselves in this predicament ($1200 estimate). Negotiate with dealer - I told him that I had another much cheaper source for CAT (there is indeed one on EBAY for $299). He said that after talking with mgr, he would do the work for $450 out the door! (turns out they had 2 of these parts on the shelf collecting dust). The last issue I have to say really helped this car was a suggestion to have the trans fluid FLUSHED. The car was slipping a bit 2-3rd gear, but after new fluid gone! Thanks so much for all the good advice!!!!!!!!!!!!!!!!!