I have a 98 SE 5 spd. Here's a little recent maintenance background. I replaced the fuel filter, cleaned the MAF, and cleaned the K&N about 5k miles ago. I replaced spark plugs with OE NGKs about 12k miles ago when I changed the valve cover gaskets.

Recently, the car has begun running very rich. It smells like cold-start idle well after it has reached operating temperature. Also, my fuel mileage has dropped a little (only premium since ownership). I've never had an OBDII vehicle run this rich with no codes. The only code I have ever had on this Max was when I forgot to reconnect the intake temp sensor after replacing the radiator about 3 months ago. I reconnected the sensor and the light went away. In the last couple thousand miles, the car runs very rich. Has anyone run into this situation? Any ideas?

You damaged the MAF in a way that it didnt trip the CEL.

Thanks for the input. It was running perfect for a couple thousand after I cleaned it, but I suppose it's possible. Short of getting my hands on another MAF, is there a way to definitively test it?

Edit: Will the voltage readings be out of the FSM specs without tripping a light?

Have you actually checked for codes, or are you relying on the light to come on?

I scanned for codes a few hundred miles back, but came up clean. I haven't tried since then.

yea if u have a multimeter, or a friend that will let u guinea pig his MAF.

I'll also add that the engine revs fine and drives fine. The only perceptible miss is a small one at idle (800 rpms) and I can really only hear it at the exhaust.

I edited one of the previous posts, but I'll ask here anyway. Will the FSM specs on the voltage be out of range without the ECU tripping the light?

No friends. Not with a 4th gen Max near me.

look into your O2 sensors aswell they could be on the way out.

as far as i know if the voltage is out of range it will trip the CEL, but the voltage could also be slightly off causing the car to think its sucking in more air then it really is causing it to run rich.

Should I follow the FSM test points directly at the ECM or is their a proven 'easier' test point for the MAF and O2s?

For the MAF u will probably have to go the ECU, and if ur already down there u might aswell test the O2s from the ECU aswell

im thinking maybe you have a manifold leak exhaust or intake thats making your engine suck in too much air. the thing is if its an intake leak it will usually cause all kinds of drivability problems. grab a scantool and check your long term fuel trim and short term fuel trim thats a good place to start

do you have any major drivability problems? missfiring, hard start, long start, hessitation?

Thanks for all the replies! I was going to start at the signal values for the MAF and O2 sensors and move onto checking for intake/vacuum leaks today. However, someone offered cash to take the ol' gal this morning. I'm gonna miss her. She was a great car.

thats a shame

I know. I want a 4th gen, but only arctic white or sterling mist. I simply couldn't find one.