did you check if the spark plugs are ALL working well?

 

Just wanted to let you know, I had the same exact symptoms. When in traffic, or at a stop - the car would idle rough when going 1-2 mph. Check engine light came on about 2 weeks later. Took it to MB and the return code was p303. Misfire on the #3 cylinder. They said it's caused by a faulty exhaust valve. $8000 job, but my warranty is covering it. Well, atleast some of it. MB quoted them 22 hrs to fix, and warranty company is saying 14 hours going by Mitchell Labor guide. I have to pay the difference if they don't agree. My car is still in the shop, should get it back next month. Hopefully this info helps you out. No one knew why my car was idling rough until the check engine light came on. You can read my thread below if you like, although in my thread I didn't post any symptoms.

https://mbworld.org/forums/new-s-class-w221/445386-2007-s550-bad-cylinder-new-post.html

 

Sorry guys I havent been on forum lately but as far as my car it still has the problem and I been to the dealer so many times they can't seem to find out what's wrong with the car because they basically just work off what the computer tells them
So I have to wait until my check engine light comes on,I have had this car for over a year with the same problem and no check engine light came out till this day.mb service sucks!

 

Have you check your charcoal filter canister shut off valve? (located on the rear right wheel well, covered by a plastic liner.

 

So a compression check would have revealed this problem, then further steps to determine the exhaust valve seat probably was wallowed out.
Cool lagoon, where were you on this one. Is the best you can say is check electrical, fuel and mecanical?? Wow go mop the floor bud.

 

Shifter go kiss your retarded attitude. Your nothing more than a second hand copy cat and a good for nothing in society, go get a job and stop seating on your fat a_ _. hahahahhahahaha.

 

shifter your not just a retired, you can't even read whats right on top your last blog. This steps are called elimination,

 

cool it, cool_lagoon. more insults will get you an infraction.

also, your sig pic, any relation to the shop in the pic?

 

thanks for the advice, i am actually enjoying the thoughts about morons and idiots, pretenders and good for nothing individuals, hahahahhaha

 

Its funny because cool guy, you didnt even know what a charcoal canister shutoff valve was, I had to tell you.

Anyhow, to the OP, any luck?

 

If this post and his history doesn't warrant a suspension, then you may as well go unmoderated.

Regards,
Don

 

Well my warranty expired and nothing was fixed they told me they can't fix it unless there stupied computer shows them the problem.i will be taking it to a local mechanic to see if he can finally solve the problem.as for that valve you guys are talking about I think that was already replaced.seems that wasn't the problem.

 

I stumbled on on this post and my car has the identical symptoms occasional rough idle and this strange down or up shift which feels like somebody has rear-ended you. So I had to post and see if this was ever resolved I realize it is quite old. Btw, my car is an 08 S550 with 160k miles. Well maintained however. Thanks in advance

 

Polo35m, did you ever find cause of idle problem?

 

Wow this is an old thread! I don't even have that car anymore I have a newer S 550 but yes I was able to resolve the problem total Hall of Fame repair. So literally all I did was clean the throttle body I disassembled it and found that the lower portion was completely choked with oil from years of residue building up. In fact there was so much you could hear it gurgling when I removed the plastic duct leading to it. I just used a rag and carburetor cleaner to wipe it out and clean it thoroughly and like magic it fixed the problem. It's a little tricky you want to do it on a cold car so you don't burn your fingers. You remove your air box you remove the mass air flow sensor and then you remove a small little piece of plastic duct and with a light and a mirror you can see the throttle body and in my case there was oil residue that had built up. It literally ran like a brand new car afterwards. And then I wound up doing this as a maintenance every year thereafter to keep it running well

 

you are the man! Much appreciated.....