I washed the car yesterday afternoon. Nothing unusual. Dried it off and pulled it back in the garage. This morning I start it and I hear a loud, fluttering noise and very rough idle. Almost sounded like as if it had a serious exhaust leak and idle was going crazy 200 RPMs up and down. I immediately turned it off. I turned it back on again and the fluttering noise is still there but the idle has steadied somewhat but still fluctuating up and down slightly. I get out and check the exhaust but notice no black smoke or any color for that matter. Pop the hood and can see the engine shaking a lot. A this point the CEL is already on. I shut it off and start it back on again. No change. I slowly back it out of the garage and coast it around the block. As soon as I try to accelerate, car is obviously misfiring and shaking so I coast it back into the garage. I call the tow service to have it towed to the local indie foreign car shop (nearest MB dealer is 400 miles away). When they arrive and I go to back it up to have it loaded on to the flat bed, car miraculously back to normal. CEL is out and no signs of any of the issue that was present 30 minutes prior. I take it out for a spin around the block and no issues. I pay the tow truck guy a $30 for coming out and I'm left wondering WTF just happened. I gingerly drive the 12 miles to work and car is absolutely normal. Any one have this happen to your car and know what it was?

 

happened to me but on my old slk. turned out i have 1 bad plug. same symptoms but it might be a different issue. have the car scanned for any stored codes.

did you wash the engine?

 

You clean the engine bay too?

 

Wouldn't a bad plug keep causing the same issue rather than completely going away? I didn't wash the engine bay or anything crazy. I dried off the few drops of water that collected at the very tip of the intake duct when I sprayed the grill but it didn't look like it had gone in beyond there. I had fueled up the day before but had driven about 50 miles with no issue either. I got an appointment with the indie shop in town tomorrow to have them scan it. Drove to and from work today after it "fixed" itself with no issues. I'm completely befuddled.

 

Could be a coil

 

^^^^ I had something similar happen on another car except it was after it had sat in drenching rain for a few days - basically there was a minor crack in a coil and moisture had seeped it and caused all sorts of havoc (trouble idling, stumbling, etc). Once it dried out after a little bit all was fine.

 

I had a similar issue. It was raining really badly and I was driving around town. There was a lot of water on the roadways and at some points, the ridges in the asphalt threw up water and caused a little hydroplaning. Some bigger puddles on the intersections but Nothing too crazy.

Anywho, drive home fine and then the next morning I went to start the car, it sounded bad and the same type of rough idle. Under 500 rpms and the check engine light started to flash. I shut it off and gave it a couple minutes.
Start it back up and same issue. I tried to drive it up and down my street but the misfire was so bad that j barely got anywhere.

Checked the obo with a basic scanner and got camshaft sensor bank 1. And obviously the misfire on the whole side of the engine. Scheduled an appointment with Mercedes and a few days later, started it up to drive up the trailer to take to the dealer, everything was normal. Decided to drive around for like 5 miles and no issues.

Canceled my appointment and it's been about 5k miles already without that issue.