Model: SLK230
Year: 1999
Miles: 202k

About a month ago, my previously perfect running SLK230 begin idling rough in the morning (the check engine light had come on at the same time), and would drive noticeably rough until I got to around 45mph at which point it was not noticeable other than a definite loss of some acceleration power. I brought it to a general mechanic and he did a check on the engine code--it indicated that there was an issue with the #3 cylinder. Spark plugs and wires are fine (not a misfire). He then did a compression check and three of the cylinders were 100%, but the #3 cylinder was 60% compression. He believed that I needed new rings and valves, at a cost of $3k which is 60% of the value of the car (something I am not willing to entertain).

Here's what I discovered in the ensuing days. If I start it up in the morning, drive it 100 yards or so, and then turn the car off, then right back on a few seconds later...it drives as smooth as silk. Then the next morning (or after work), rough idle/run, then restart after driving a bit, then fine. Repeat. It almost seems electronic but the mechanic said it wasn't. It's always rough when I leave it for a number of hours, but if I drive to the gas station, turn it off for a few minutes, then on again, it runs fine. I don't think it can be the rings because that doesn't correct itself as far as I understand it. Could it be a sticky valve?

Any thoughts would be greatly appreciated.

Sam

 

Post the code. Swap the #2 and #3 coil, clear all codes and see if you get a #2 misfire code. This will tell you that the coil is bad. Change out the plugs with some fresh ones. Also clean the MAF with some crc MAF cleaner. Run some injectore cleaner through the system (every other tank of gas)

 

My coolant system was leaking just a bit, so I ended up putting in some coolant system sealer (I forget the brand). Anyways, the engine now runs smoothly (even from a cold start). Can anyone figure out why that would've "fixed" the engine problem? My father and I are at a loss.

 

It could of been just a bad connection contact on No.3 injector, or any sensor (maf cam crank) and by slamming the hood corrected itself. What was the fault code? I bet Mercedes dealer would be cheaper then your mechanic (25hrs.of labor?!).