My wife drives a 1998 C230 we bought a year ago. Its got about 65k miles on it. About 5 months ago the CEL light came on for a day. Recently it has come on and stayed on for a month then went off. Its back. The Autozone pulled the P0170 code. the car runs fine. It even passed Massachusetts emissions with the CEL on. The Autozone guy cleared the code. If the car runs fine and it comes back, do i really have to do anything if it runs fine, or it is it possibly a matter of time when it will start running lousy.