91 300E in very good condition with 124,000 on the clock. Check engine light came on briefly today. The car was warm at the time, but had been sitting about an hour in 70 degree weather. After the hour of sitting, I got in with some friends and drove semi-aggressively in order to keep up with another car we were following. After about 30 seconds, the CEL came on - I had never seen it before, so I didn't know what it was until we stopped approximately 5 minutes later. Total drive time was about 5 minutes, then I turned the car off. When we got back into the car an hour later, I started it up and the CEL was not on anymore. So far, have driven another 20 miles tonight and no sign of the CEL.

I just did a search and found a few really helpful threads regarding CEL diagnostic codes and what they mean. My question is: do I need to start troubleshooting the cause of the CEL light yet? It only came on once very briefly and isn't on anymore. Should I wait to see if it comes on again and then worry about it?

I bought this car almost 3 months ago, have put on over 6,000 miles without any problems whatsoever. I have the typical intermittent high idle which I mentioned in another recent post (1800 RPM in neutral, about 1000 in gear) and it occurs maybe 1/3 of the time - the other 2/3 of the time it idles flawlessly. I just haven't gotten around to checking into the high idle; Duke mentioned the TPS and I was going to check that this weekend, but due to busy schedule it looks like I won't get to it until the holiday weekend.

Could the high idle have anything to do with the CEL? Could it have been caused by my somewhat aggressive driving without allowing the car sufficient time to warm up? I mean, I was pegging the gas right after startup, but it's not like the car was cold or anything - it still had a fair amount of temp on the gauge. Is the car still safe to drive? It sure runs fine, and it ran fine even while the CEL was on (wasn't experiencing the high idle at the time).

Can anyone provide any advice? I'm starting to get paranoid; maybe my pleasant-running car is about to turn on me...

Thanks!

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

My theory has always been if the check engine light is not going to behave consistently I'm not going to worry about. These things do have random hiccups now and then that are not repeated. You might pull the codes to see if there is anything there but I wouldn't worry about it until it comes back and stays on. Could be somehow related to the idle issue but doesn't seem likely given that they don't occur in sync. I'd be more worried about attacking the idle issue if I were you.

Check the archives on how to check the ECU for fault codes. I believe a 91 has the button and LED set-up near the X-11 port or something like that. Maybe only California 91s have the feature.

Put the key in the on position (engine not running), hold down the button for 2 seconds, count flashes, repeat until you're back to a number you've seen. Hold the button down for 10 seconds after each code to delete the code once you've noted it.

Sixto
95 S420
87 300SDL

OK, it has been about 250 miles since the CEL came on. It hasn't come on again since, and the car is running fine. At my last fillup I registered 20 mpg in mixed driving (my typical average). Oddly enough, the car hasn't suffered from the high idle ever since the CEL came on. I'm sure this is just coincidence and it will soon start idling high again...

Anyway, the car really seems to be fine. But I am a paranoid worry-wart, the type who would fix something BEFORE it breaks if at all possible. Should I bother trying to hunt down the diagnostic code for the CEL?

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Seeing as it costs you nothing to read the codes...

Sixto
95 S420
87 300SDL

Check the gas tank cap for correct seating. could be that you did not re-install correctly it at the last fill up. Otherwise I would not be concerned if the CEL stays off. The CEL on my Wife's 96 Nissan Maxima will come on for a few weeks and then shut off without any help ($$) from me. In the beginning I would take it to the dealer and be charged for a new O2 sensor. Lately I just wait a couple of days/weeks until the computer makes an adjustment, and the light goes off. This Maxima has 125,000 miles and other than too many early 02 sensor replacements it has never given any trouble.
Mark