Donnymac

Stopped at red light. Motor purring perfect. Motor/car shimmies for 2 seconds then smooth as silk. But.....check engine light is now on.

Drives home perfect. Restarts perfect but CEL is still on.

No recent oil changes or fill ups/tank half full.

thoughts?

joonman

I recently purchased 2011 S450 and experienced a similar issue, but no CEL. This is what I have done so far. First, I did relearn idle process - put the key in Position 2 (just before the Start) for 1 minute, turn off the key. Second, I put a bottle of injector cleaner and drove for a while. Idle is now much improved. However, I still feel the vibration periodically, although much less frequently. Next steps for me, based on research I have done would be:

1. Clean MAF sensor
2. Clean Throttle Body
3. Check spark plug
4. Replace fuel filter
5. Check the motor mount

Donnymac

Mine did it once only during idle. Lasted 2 seconds. Shook,the whole car. Was like half the spark plugs quit Then CEL was on but motor running as if nothing had happened.

The next day, CEL was off and no repeat has occurred. I have no clue as to the solo shimmy that threw the CEL. I plan to run codes later today.

fresh motor mounts make a world of difference to general performance. Plugs too. Those are necessary maintenance items.

joonman

I cleaned the MAF sensor today. At the same time, I decided to remove a couple of spark plugs to check. I am not sure whether these sparks plugs were ever changed. Spark plugs had the Mercedes logo with NGK stamped on them. They did not seem new but gaps appear to be fine. Since this car only has 96,000km or 60,000 miles, I am suspecting that they may be original plugs. What was concerning was I noticed that both plug's thread were oily, but not the plug body itself. However, plug tips were fine. Do I need to change all plug seals? How complicated is that to do?

Donnymac

I can't answer that. This Forum is full of info. I would bet there is a spark plug change thread.

i had my plugs, motor and trans mounts plus A arms/ball joints done all at once by Austin TX Dealer.