AndyIQ

Hi,

My name is Andreas I have a 2008 CLS 63. Just for reference I bought the car from the son of the original owner. The car is near mint, always garaged and 100% dealer maintained with records. The car is 100% stock, no mods. I am posting today because I need advice.

18 months ago the car would occasionally (every 15 starts or so) idle ruff when cold starting. The only way to fix it was to shut the car off and turn it back on. I told the dealer and they said no code = no problem

12 months ago: No change in the frequency but definite change in severity (much rougher idle, clear misfire on at least one cylinder). The CEL would come on but when I would restart the car it would be gone and all was fine car was smooth again. I took the car to the dealer, they replaced coils

8 months ago: No change in the frequency slight increase in severity (rougher idle, clear misfire on at least one cylinder). The CEL would come on and stay on, even after I restarted car and the car was running smooth. The dealer determined the problem was caused by a fuel injector leaking onto the engine wiring harness. So dealer replaced both (had the car for 2 months).

6 months ago: Got the car back and was disappointed from day two when this rough start occurred. The severity was less then it had been but still a misfire and I had to restart the car to make it go away. The dealer did a code scan and found nothing.

I continued to drive the car a few times a week (less than 2k in 6 months). The car continued to have rough idle starts with the occasional CEL that would go away with the problem once I restarted the car. This last weekend I drove the car 200 miles out of town, everything went fine until I went to start the car the next day. I started the car and it shook severely (worst I have ever experienced), had I been holding a cup of coffee I would have spilled it. The CEL light was flashing. I shut the car down within 5-10 seconds and restarted it. This time it did the same exact thing upon restart. Only on the second restart did the car go back to normal with the exception of a check engine light now on solid. This felt like a misfire on multiple cylinders.

The car went back to the dealer, They have had it 5 days , They believe that head bolts are bad and coolant is leaking into cylinders when I park overnight causing the misfire. The problem I have with this (besides the cost) is:
1: head bolts have already been replaced as a precautionary measure.
2. The car starts in a garage and I have never seen, or smelled any steam, coolant, smoke, anything at all when starting.
3. The coolant level has never been low and I check it once a year or every 10k miles.

The dealer did say that there is a chance that the head bolts are fine, at that point I would have spent $1600 and still have a broken car. I am tired of throwing money at this so if anyone has any experience with similar situation I would love to get some advice.

PieRat

Sounds like you need to take the car to a different dealer/mechanic. Doing a job to test a diagnosis is something amateur mechanics at home do(me). They dhould be testing for gycol in the oil to confirm contamination before they go doing the head gasket. I cant speak to m156 but similar issue on my cls55 was caused by an air intake leak tripping ecu. Would be cruising and the car would suddenly idle rough af and id have to restart it for it to run fine. Basically i believe if the car is constantly seeing inputs from sensors that dont add up they revert to a backup map, my cls55 is heavily modded so this map wasnt tuned for mods. As i said this is the m113k engine not m156 so take it as food for thought.

Another note is e63 forum is a lot more active and has dame engine. Id search that forum and post there.