2005 Chevy Cavalier Check Engine Light

I bought an '05 Chevy Cavalier with about 38 thousand miles on it. Somewhere between 39-40 thousand miles the check engine light came on. I came online and read all the stuff about the emission sensors and all that jazz. So here is what I did...

1. Took it to Autozone and got the code erased after checking the obvious ofthe gas cap. It stayed off for a few days then came back on.
2. Took it to my mechanic friend and had him check it out and he also reset the code and drove it and said he didnt see anything wrong with it. He left town and told me if the engine light came back on to bring it to him after he got back. About a day later it came on while he was out of town. And wouldnt you know it by the time he got back it went off by itself.
3. For the next month or so the check engine light would come on for a few days and then magically go off for a few days. At almost at 41 thousand miles now and the check engine light has been on consistently for two weeks but every day I expect to go off.

The one thing I thought I might have noticed was that ever since the first day the check engine light came on...when I start it up in the morning the engine seems to run loud for a few miniutes. I'm not sure if it was always that way or if it just happened to catch my attention because the engine light came on.

Any thoughts on what might be going on? I'm a poor college student so any cheap methods of fixing it will be greatly apprectiated.

On a side note if you happen to know how much it would cost to put in automatic locks on my car (a four door) please let me know.

what codes did you get when the check engine light was on?

Jake already asked just what I was thinking. Instead of erasing the codes and turning off the MIL, read the code information. That will be the best hint about the problem(s).

...any cheap methods of fixing it will be greatly apprectiated.

The least expensive way to fix it will be by diagnosing the problem, and repairing or replacing only the part(s) needing it. For example, an error code indicating a problem with the EGR valve doesn't necessarily mean the EGR valve itself is bad, but that there is a problem with the EGR system causing the error code. Replacing the EGR valve as a result of reading that code might be a more expensive route to the solution.

As for the power/remote locks, the wiring for the locks is probably not included in the door harnesses. The least expensive way would be to scavenge the necessary switches, lock motors (solenoids), door harnesses, and interior door trims from a donor vehicle in a salvage yard. If you want remote entry, you'll also have to get the remote receiver and its wiring, as well as a remote transmitter (key fob). Since you're evidently on a tight budget, using the door key might be the most cost-effective method of gaining entry for now.

i put keyless entry in my 4 door with 4 actuators ($15 each) two wires thru each door boot and 2 relays to drive the actuators - it cost me 60 dollars and 3 hours

If the code indicates an emissions problem ,I think I would be checking with a dealer ,being that the car is only 2 years old. Warranty on some things (emissions) is quite often a higher mileage coverage.