japd99

Mercedes cannot figure this one out! I have a 2007 S65 with 65K miles. Just had service and spark plug change, hoping it would solve the issue. If I run the car to normal temperature and stop for 15-30 minutes, it has a problem when I start back up. Essentially, I start the car again and the RPM's go real low to where the car almost shuts off and is rough. It then spikes up to 2K RPM or so and evens out to normal afterwards. It's a little unnerving as sometimes if I am in a hurry and put the car in gear it can essentially "take off" if it is doing this.

Any thoughts or ideas on what this could be? I do not get a check engine light and supposedly no "codes" are detected at the Mercedes service department.

Thanks for your help!

shardul

iTrader: (1)

check for vacuum leaks

japd99

I took my car in again to Mercedes and told them to check for vacuum leaks. They said that I could get a "check engine" light if that were the case. They did find that a couple of engine mounts need replacement and that may explain the "roughness" at idle. I'm not sure how this would cause the car to almost stall. They are also going to replace the rear engine seal due to an oil leak. What do you guys think? Does this sound legit?

F1BHP

Sound like dirty maf sensor. Get some maf cleaner and see if it fixes it.
Do yo have k/n filters?

jettbird

Maybe coil bank issue. Does it code misfire? Mine did and it went away after replacement of left bank pack.

japd99

A week and $4500 later (covered by my aftermarket warranty ) I got my S65 back. The car is running like new again. The engine and tranny mounts were all replaced. It is smooth and so ridiculously fast! I am extremely pleased. Interestingly, yesterday my friend let me borrow his Ferrari FF. Yes, the Ferrari is a fast ride and I loved it but my MB is so much smoother and seems so much torquier! Yes, I know...Different cars.

Hopefully good to go for a long time now. One piece of advice- Get an aftermarket warranty on these cars after the original runs out. They are super expensive to maintain, especially if you're picky like me and want to keep them perfect. My '07 has 65K on the odometer and looks like new. The best thing about these cars as opposed to a Ferrari is that I can drive it regularly and not feel as guilty putting miles on the car.

Only other thing I want is a thicker steering wheel. The wood looks nice but feels so thin compared to newer cars, it almost makes the car feel wimpy. Any ideas of where I can pick up a nice steering wheel for this thing?

F1BHP

The mounts would not cause fluctuating RPM's. Sounds very strange unless they did other work while they were there.

s5benzo

Most company's don't warranty v12s ! What company is your warranty through japd99?

V12TTenthusiast

Fidelity will, they covered my car including that crazy engine mount job and ABC issues like the pump/strut/valve block. I got a good deal for 4 years / 50k miles full plat. for about 4 grand, but my mileage was really low.

V12TTenthusiast

Engine mounts do cause rough idle on these V12, if it was minor fluctuating in the RPMs then mounts could have been the issue but if it was really jumping more like coils or a bad crank sensor or god knows what else. But after I did engine mounts last summer my car road like a new care

JohnLane

I have a 2008 S-65 with 62,000 on it.

Smells as as similar issue described above. Perfect drivability from stone cold. Park fully warmed up for 15 minutes to an hour... 'Hot soak restart' makes for very rough idle... Has done this many times since I purchased the car. Today it lit a check engine light. Misfires for virtually every cylinder+ multiple misfire codes. Coils, plugs are fresh. Runs perfectly except for the hot soak restart.
MB tech speaks of paint they got to apply to ring gear or some such when they were close to new.

Thoughts?

This is is not engine mounts. It misfires.

Thanks.

alexanderfoti

Is your ignition transformer new also?

JohnLane

ItalianJoe1

It's the fuel pressure. There's a bulletin on the older cars, I had the exact same issue on my CL, had to replace the pump/regulator/filter. Got way better.

The root of the problem is ethanol in the fuel. It boils at a lower temperature than gasoline, so you get a vaporlock issue when it heat soaks and can't get liquid gas into the engine. It wasn't present in pump gas 10 years ago. They've raised the base fuel pressure so it doesn't act up as much anymore to compensate.

https://mbworld.org/forums/s-class-w...ngine-out.html

Last post on the first page, the bulletin is linked.

JohnLane