I have a 98 C230 with 80,000 miles. Recently the check engine light has come on and there have been days on and off in the past week where it has run badly. I.E. Lack of power, missing, and hesitation shifting. I had the dump from the computer done at Advance Auto and the only error that it had was a "Misfire on Cylinder 1". I replaced the spark plugs, as a start, and the next day it seemed a little better. Today, when it was started it idled very smoothly but when the accelerator is pressed "at all" it starts to die out and miss. The harder you press the accelerator the worse it gets. I performed the cheapest and easiest fixes that I know. I replaced the air filter, sprayed out the throttle body with choke & carb cleaner and replaced the fuel filter (under the car in front of the rear axle). Before I start throwing parts at it, does the fact that it had the "misfire on cylinder 1" lead us to believe that it has to be a coil or wire next? Or is a dump from an auto parts store not reliable? I am 3/4 of the way through the tank of gas on which these symptoms started. Could it just be bad gas?

Any help you can give would be appreciated.

You'll have to find out WHY the misfire is happening. That car can have bad misfires from corroded plug ends, and it's a common problem. You could keep throwing parts at it, or you could invest in some good diagnosis help from a mechanic. My car had both a misfire code and a fuel trim code and we tracked down the fuel trim to a bad Air Mass Meter and the misfire to bad plug ends. What a good mechanic will do is replace a suspect part with a "known good" when they've narrowed it down, and see if the problem is solved.

Did you spray "choke and carb cleaner" (of which you have neither) into the AMM? If so, you might have wrecked it. Is the CE light still on? If so, read the codes again.

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John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif

With that great dump you got did you get some adaptation readings. The misfire is a result not a cause, most likely. So far you have a sum total of no information. Gotta have somewhere to start. Could be ignition could be fuel, I'd start with adaptation for first smell.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Can an OBD-II reader give adaptation values? I think you need SDS for that?

Steve, if the only code thrown before was a #1 misfire, could there be a fuel trim or other reason for the misfire that wouldn't be severe enough (crossing threshold) to cause the misfire? If so, that makes sense. The good idle and terrible throttle tip-in performance seem like much more than a #1 misfire.

Are there adpatation values for ignition? When we were diagnosing my codes, we read the fuel trim values and quickly tracked down the AMM, but the misfire was quickly evident when checking the wires and I don't recall any other adaptation values being read by my mechanic.

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John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif

Update:
Thanks for the quick responses. I have come up with a few more things. First off. To answer a couple of your questions.

The dump I got was not from a SDS and I did not get any fuel trim readings.
And I sprayed the cleaner directly into the throttle body without the breather tube in place.

When I replaced the plugs. plug tip on #1 was more corroded looking than the other 3 by far. (maybe misfire code?) Maybe I should look at replacing the plug ends. (#1 has just a wire on it, no coil sitting on top)

But another symptom that my C230 has had for at least 10,000 miles is that there was a BAD hesitation at around 4500 RPM when passing. (AMM?)

I saw the trick where you put the AMM in a plastic bag with rubbing alcohol and shake it and then dry it and reinstall. I tried it. Prior to doing that, the best I could get from my car was about 1000 RPM, after reinstall, I was able to drive around the block a couple of times at up to about 3500 RPM's with very little missing and actually almost drivable. Impossible before.

The CEL is still on and there is definately something wrong with the AMM. I am going to replace that tomorrow, and then see where I am. At least then I can respectably drive it to a mechanic with the proper diagnostic equip.

If I get it running halfway decent, should I attempt to disconnect the battery and clear the CEL before taking it to the shop? Or just leave it alone?

You guys have been very helpful.

Never heard of that solving any problems, but I could be wrong. You'll need to use SDS to get real diagnostic info. The reason AutoZone etc. charge nothing for OBD-II code reading is that in many cases, it's useless info.

Classic AMM symptom. An AMM showing that can have an adaptation value not sufficient to trip the CEL, but cause running problems. Been there.

Cleaning an AMM does not work and is a very short term solution at best, as you have found out. It sounds like your AMM is bad if the "cleaning" helped at all.

Disconnecting the battery is not a solution to a CEL under OBD-II. If you actually solve the problem, the CEL will go out on it's own after a certain number of key-cycles/time/etc. without the problem occuring. Without reading your adaptation values I would guess that you have a bad AMM and probably plug-ends that are in need of replacement. Driving the car with a bad AMM is not kind to it as it cannot operate within the proper fuel/air ratio range.

I would say that you might want to find a knowledgable mechanic. Contrary to what many say, paying for good diagnostic help can actually save you TONS on parts "throwing" as per DIY. The SDS is a valuable tool that can provide incredible information. I had a CEL the other day and my mechanic had the diagnosis in less than five minutes and within ten minutes the problem was solved (the little "tick-tick-tick" emissions valve who's name completely escapes me right now...) The half-hour labour charge was CHEAP compared to the mess I might have created had I tried "tracking it down" myself.

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John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif

Thanks for all of your help.

I purchased the Air Mass Meter from the dealer. It was 414.00 with a one year warranty and the cheapest one I found online was 380.00.

The car runs like a dream now. I purchased the car with 70,000+ miles on it and it has never run as well as it does now. The CEL cleared after I ran some errands at lunch and everything seems good.

I am still going to replace the plug ends just in case that is the reason that plug #1 looked so bad. They are due for a replacement anyway.

Just as a side question. The dealer had 4 different AMM's for my car, depending on the VIN #. AutoZone only offers 1 also made by Bosch (same price as dealer) . Is there that big of a difference between the 4? I would never take a 400.00 chance.

Thanks again.

I was just waiting for the "runs like a dream now after replacing the AMM"

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99 C43
98 S420
99 C230K
01 C240

FYI, my 97 required new resistor tips/caps when the plugs were done last February, at 80k, due to the same symptoms you described.

My AMM went south this fall at 105k, and that was the flat acceleration at 4500rpm.

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL