Hi - Check engine light (not service) has come on twice in the last couple weeks. Both times while driving in stop and go type situations (heavy traffic). Stayed on for a day or two, but both times after a good run on the highway (20-30 min @ >=70mph) and after shutting the engine off, the light clears. I have not had the code read yet. Any thoughts? Oh, also, will the code still be set, even though the light is off?

Thanks,
patwa

One of the few nice things about OBDII.... If the problem corrects itself (like a temporary misfire, or you have replaced a defective part like a bad PNP sensor) the OBDII system can reset itself after so many cold/hot driving cyles.

I would get the code pulled as already suggested since it has happened twice. Chances are this is an early warning of something getting ready to fail permanently.

DEWFPO
--
1998 S90 071,245 and 1995 964 154,100

This time when the light came back on I had the code read. p0303 - misfire on cyl 3. Car was really running like crap. The other times it seemed to "work through it" and all was well. Today I couldn't shake it. Rough at idle. Rough at speed. Couldn't get much power. Haven't looked at the plugs yet. Is that the most likely issue?

The most likely cause of a misfire that you can't shake in not the spark plug.

It's typically :
- a bad coil
- bad Power Stage Unit
- the wires to that coil

DEWFPO
--
1998 S90 071,245 and 1995 964 154,100

Yes the code will still be set. If the problem corrects itself the light will go off but the code will stay for a long time. You will be wasting money if you take a guess at some part to replace before you read the code and find out what area is having a problem.
--
'96 965, 16' wheels, rear 18mm bar & Koni + 204HP cams at 124K. Had '85 745 Turbo Diesel for 200K.

The codes seldom go away by themselves, check and clear them. I have had the cel come on when the generator/altenator was overwhelmed with power requests in stop and go traffic with the AC and fan on high.

Klaus
--
98 V70Rawd(101Kmi), 95 854T(85K mi), 75 164E(173K mi)