RE: 1998 check engine light?
It's going to go off when you don't keep the minimal oil change constant or your air filter gets so dirty, to the point the PCM cannot reduce the F/A mixture any lower. I do mine every 2900-3000 miles and reset it myself. Just turn on key, push gas pedal 3 times, holding it down on the third. My wife resets it for me, I just change the oils and clean the K&N but I am sure that is the procedure. If I am wrong, trust I will be corrected. As for the Codes; since your Pre 99', If you had an issue with a system component, I believe your system would let you know by a FLASHING "check system," light - ie; 3 flashes - 2 flashes - 3 more. You would then look up the code that is represented by a 3-2-3 flash. A constant light is more than likely from the guy who changed your oil and his failure to reset your system. Again, if I am wrong, trust I will be corrected. You can take it to any car shop and have the light reset for free. Just tell them you just changed your oil.