Hi guys, recently i've noticed a rough idling when the car is in park. it almost goes away when the brake pedal is fully pressed (in 'D'). as soon as i let off the brake & when the car is rolling forward i feel the roughness/vibration again until the car speeds up. the braking and slowing down has been quite rough and jerky as well and the car doesn't slow down smooth (I have brand new brake pads and disc). however i feel stopping is a lot smoother when i put the car in neutral (while rolling) and then brake.
i have had the pedal accelerator module and MAF sensor replaces 10 months ago. then just recently MB dealer replaced the RH oxygen sensor, 16x spark plugs, fuel filter and air filters. this has solved the ongoing acceleration problem (misfiring etc) which i had for the past 4 years. however this rough idling is something new. i had it checked by MB mechanic and they say there is an air leak present in intake manifold assembly and now want me to spend over $4k to get a new assembly. i have been reading other threads and they all pointed to engine mounts as a reason for rough idling. this morning put the car in R/D and revved the engine. i could see the engine moves up at one side about an inch maybe. is this the sign of bad engine mount? do i have to trust the MB mechanic and fork our $4k for intake manifold assembly? can't an air leak be fixed (sealed) instead of a whole new assembly? any help would be really appreciated.

 

MB dealers dont "fix" things, they replace things.


Its easier for them to replace complete assemblies rather than attempt to repair an old part.
Find a good independent repair shop who actually knows how to repair parts rather than replace/swap parts