Mercedes C230 runs rough, then smooth, then rough

I’ve got a merc C230 Kompressor that has 174k miles on it. The car typically runs really well and is not underpowered or anything. Last weekend I took a road trip that was 400 miles or so. The car did fine for the first 300 miles but then began running rough and was underpowered. Was acting like there was a fouled plug. I pulled over and stopped the car where it sat for about 5 mins. When I restarted the car, it was back to normal, with a smooth idle and not underpowered. It ran fine for about 30 mins and then began running rough and underpowered. I find that when it starts running rough, if I stop the car and turn it all the way off for at least 60 seconds, then when i turn it back on it will operate normally again for a bit. This also only seems to be happening when its really hot weather, 90 degrees F or higher. Any ideas?

Sounds like one of your ignition coils is beginning to die.

I would replace the spark plugs and the offending coil. I believe your engine has coil over plug system…which means No distributor, no spark plug wires…Just coils…over plugs.

If one of the coils is failing…you should throw a code, but I have seen many engines NOT throw a code when one of the coils shorts to ground (usually from oil in the plug well from a leaking valve cover gasket) When they short to ground you dont get a code bec technically the coil is firing but that energy is going to ground instead of thru the plug.

Id check for codes and if there are none…pull a few coils and make sure there is no oil in the plug well…or any other liquid. If you do have an engine code…it will point to the offending plug/coil combo…after that…just replace whatever one is misfiring. If NO codes…you need to see if you have anything in the plug well that would short the coil to ground. Replacing the plugs probably wont hurt you either…when were they last replaced? Use the OEM plug as well…almost surely some form of Bosch Platinum…or other high quality plug…Do not skimp on the type of Spark Plug. They dont wear out often and need to be of the Quality commensurate with the engineering in that Engine…which is to say…High Quality.

Blackbird

What model year?

There were at least 2 different body style C230 Kompressors

And there were 2 different engines

About those plugs . . . I highly recommend using only the plugs specifically listed in the owner’s manual. I don’t think your engine is going to behave if you use cheap Champion, for example

thanks for the input guys. I was actually suspect of the coils too and thought that might be a good place to start so I appreciate the advice. For sure, i’ll put the good plugs in, it’s probably the last time they will get changed on this car so might as well go for good ones.

db4690 - its a 2004 sedan

@GreasyKnucklesGuy

Thanks

Now I know that you’ve got a 271 engine in a 203 chassis . . .

This is slightly off-topic . . . but are you fairly certain that all the service campaigns and/or recalls for your engine have been performed?

There were quite a few, and some of them were for driveability and engine mechanical problems

By the way, would I be correct in assuming that the check engine light is, or was, on at some point?

Was the check engine light ever flashing?

If you’re not sure when the plugs were replaced last time, it might be a good idea to just get it over with

If you could get the codes read for free . . . at autozone, for example . . . that would be great

Don’t get too frightened . . . this engine was known to have valvetrain issues. Low compression due to valve and valve seat problems. Hopefully that isn’t an issue in your case

In all likelihood, your problem is something relatively simple