My E320 has 122k miles on it. Runs pretty well but it has an annoying idle when I shift it into gear. When I back out of the garage the idle seems so low the whole car is buzzing. When I shift it into Neutral, the idle speed goes up and the buzzing disappears. In gear, the idle speed seems to be barely above 500 rpm, perhaps 550. In neutral the idle speed seems to be about 800 rpm. Is this normal...I hope not!

 

it's your motor mounts. I had the same problem about a year ago.

https://mbworld.org/forums/e-class-w...or-mounts.html

 

Thanks for the input. I just cleaned the MAF sensor and replaced the plugs with Bosch platinum fusions +. No real change that I noticed. Perhaps a little "perkier", but that could be wishful thinking on my part.

 

As Siopaolover said, check you engine mounts, if you see that they are leaking oil, they are bad. Do both sides even thou only one is leaking.

 

if youre not getting some sort of CEL, I would agree with this guy.

 

Among all suggested by earlier responders, coils and engine mounts are the usual culprits. At the least, coil change did solve the problem but only after engine mounts were replaced. $$$

 

Hey Siopaolover, I feel i have got a problem with the engine and the transmission mounts. At cold startup, there is rumbling inside the cabin. The rumbling soon disappears when putting in D and driving off. The rumbling is lower at idle or in neutral when the engine is hot enough.

Another thing. The transmission shifts very smoothly when accelerating, but makes light thuds when rapidly braking and coming to a halt. There is a clicking noise that can only be heard from outside the car while shifting.

I have a very strong feeling I should replace the tranny and engine mounts.

Any inputs will be very helpful.

 

The rumbling that you mentioned while in idle and startup is common with worn motor mounts.

I'm not too sure about the transmission problems though, sorry.

Welcome to the forum, btw

 

Thought you'd like to know that you were spot on. It was the motor mounts. One was shot and another one was ready to go. Makes all the difference in the world. Thanks.

 

It was the motor mounts. Makes all the difference in the world.