Sir, the check engine light may come on for various reasons. I have a 99 Monte Carlo, with 165000 Miles and I love it. My check engine light is still on after having new plugs and wires. I was told it was because of a misfire. Car still misfires, I think it is a bad censor though. You should really have your car checked out, I am sure glad I did, I found out that my plugs have never been changed, after 165000 Miles. yeah, that is really bad on the motor. If you don't want to go to the mechanic, you should try and get new plugs and wires, or maybe a basic tune up and see if that helps. I hope I helped you out some, if you want you can comment me at email@example.com Oh, and do you know NOT to use green Antifreeze, I found that out when I went to the mechanic also. Use Dex Cool Antifreeze, The Orange or Pink Color kind.
I own a 98 Monte with 47.000 miles. No problems (yet) with the troublesome intake gaskets on the 3.1. Great running and handling car, I would highly recommend to anyone.
I bought a 1998 Monte Carlo with 160,000 miles on it. It now has 192,000 miles on it and all I have done is replace the belt, battery, brakes and 2 tires. I had the transmission flushed (was a little worried about doing that) and that about covers it. The CD player quit working and the console lid broke off, but I can live with that. I'm now going to hand it over to my son to drive until it dies. It's been a great car, but has also had great maintenance from the previous owner and myself. Great highway mileage...29-30 and a pretty comfortable ride.