I have a 1999 eclipse RS 2.0L with an odd problem. The Service Engine light comes on at odd times, stays on for a short time, and in one case for 3 days, then goes out. Shop can't find anything wrong with the car when placed on the computer.

We ran the car up on a lift and did a visual inspection and the only thing that appears to be 'unusual' is the o2 sensor on the exhaust has slipped it's plastic casing although the wires are still firmly attached to the sensor itself.

The shop I go to says that as long as the wires are attached, the o2 sensor should operate fine and I shouldn't need to replace it.

Now for the really odd part. When the service engine light is ON, the cars performance is significantly better, having greater powerband acceleration than when it is NOT on.

I'm a new owner, I have only owned this car for about 6 months and am not familiar with the car enough to be able to make an informed opinion on what may be happening.

My only previous experience with a sport compact car was my 77 celica. Basically, i'm clueless on what to do and would like some advice. I'm not sure my shop guy is on the up and up with me, but the closest shop that deals specifically with foreign models is a 2 hour drive away and I don't generally have that kind of time during 'business' hours to make it there.

Dragon

i say just take it to your local autozone and rent a scanner and hook it up to see if you get any codes. who cares what your mechanic says. See if you get some codes this time around.

Thats an idea I didn't think about. next time the light comes on I'll do that and see what we get. I think my shop guy is more familiar with Mopar anyway. Guess i'm gonna have to look around some and see if i can find a decent mechanic around here w/o having to travel 120 miles. I can do basic mainenance on a car, oil, air filter, antifreeze blah blah, but past that, i'm somewhat lost (read that as, put me in the woods 100 miles away from anything, blindfolded and naked and I'd have a better chance of finding my way out, than I would repairing an engine.).

Dragon

p.s. Nice looking car btw.

Could be that the front O2 sensor is on its way out. Once they get up there in age, that's one of the first things to go. When the ECU loses primary O2 signal, it switches to a default fuel trim which is overly rich in order to prevent detonation.

If you're running this rich, the car might feel a bit peppier, but you'll notice some black soot on the rear of the car after a while. This is unburnt fuel.

I can't say, for certain, that this is the problem, but when the front O2 goes out, it tends to act up a bit and kinda wigg out.

Originally posted by DR1665
Could be that the front O2 sensor is on its way out. Once they get up there in age, that's one of the first things to go. When the ECU loses primary O2 signal, it switches to a default fuel trim which is overly rich in order to prevent detonation. If you're running this rich, the car might feel a bit peppier, but you'll notice some black soot on the rear of the car after a while. This is unburnt fuel. I can't say, for certain, that this is the problem, but when the front O2 goes out, it tends to act up a bit and kinda wigg out.

Thats what I was going to say. I never had the boost in performance, but when my front o2 went out, I got the CEL that would go on and off randomly for a short while until it finally just stayed on.

my car had that problem too my chicks dad has a computer to find the problem it was a bad throttle position sensor $15 part he could look up the last code used on the ecu so im guessing your mechanic can too