Hello All,

I have dug through so many threads and spent so much money to try and find a possible solution to my issue, and still no luck.
Here are my symptoms:
1. After a cold-start, there is little to no idle.
2. After driving it for less than 2 minutes, there is pretty severe shaking whenever I come to a complete stop. It doesnt matter if Im in P,D,N, or R, I still receive the same symptoms.
3. There seems to be a bit of shaking/stuttering when initially stepping on the gas pedal, but the shaking goes away after about 2500 RPMs.
4. There also seems to be a bit of shaking right before a complete stop while the car rolls to a stop.
5. There are NO CHECK ENGINE CODES

Here are the things that I have done already:
*Replaced all plugs and coils.
*Replaced CATS
*Replaced upstream O2 sensors.
*Replaced the air intake manifold
*Replaced MAF
*Replaced tranny and engine mounts
*Performed a smoke test for vacuum leaks (none)
*Cleaned injectors
*Used a TON of Seafoam

I feel like Im all out of options now
Should I try replacing the wiring harness next?

Vehicle Specs: 2002 Mercedes S430
98k miles on it and Im the second owner.

(PS: The original owner had the car sitting in one spot for quite a while if that matters)

you will NOT fix this car by throwing parts at it.
Get an SDS diagnosis!

That was the first thing I did. Nothing in there that identified the problem directly and every time they would tell me to try changing something different.

Has the engine compression been tested? Has a 'power balance test' been conducted? What are the results. From your description, there seems to be severe misfiring. Fuel injectors, fuel supply, ignition failures, or bad camshaft or burned valves.

Throwing parts (try this, then that) is expensive and only sometimes works. Testing the compression, and then vacuum at idle gives a good idea of Mechanical condition of the engine.

maybe a bad valve lifter ?
" but the shaking goes away after about 2500 RPMs."
maybe it pumps up with more rpm/oil pressure and goes away.
if the car sat for a while before you owned it, one or more may be collapsed or sticky.
my first guess, anyway.

Do you have new fuel in it or the original from previous owner?

I tested the engine compression when switching out the spark plugs. The engine is solid, and clean from what I can tell when replacing the intake manifold. I mean, only 98k miles and it seemed to have been well taken care of.
I have gassed her up with premium gas several times now, and have cleaned the injectors during the intake manifold replace.
I also see a loss of power during the shaking if that helps narrow it down? (Dimming of headlights)
I think it may be something electrical at this point since everything mechanical that logically would affect this has been replaced. I guess MB aren’t as simple/straight forward as other cars.

i just don’t understand how it’s not triggering any check engine codes with such drastic idle shaking.

Yes low voltage can cause rough running

WHICH cylinder(s) are misfiring? Always the same one(s) Why are no error codes being set? Did the problem happen suddenly or start gradually and get worse with time and miles?

'Sticky' fuel injectors can be slow to open and not deliver enough fuel to fire at low RPMs since the Open pulse is so short. Check the fuel pressure at idle to ensure it is high enough. Did the problem start suddenly and get worse with time/driving or? A single slug of high gum gasoline can plug fuel injectors with gum which 'retail' injector cleaners will not clean-up. BK-44 is THE injector cleaner to use. I have used acetone (1 qt/1 gal) to clean up a really fouled set for a guy. It worked. The alternative was to replace all 8 injectors.

Check O2 sensor outputs to see if they are proper---not 'pegged' against 'Lean adjust max" which would cause a lean mixture Today's gasoline has ethanol in it (some up to 15%) or more if miss-blended. That will cause 'lean misfires'
IF for some reason the Crank position sensor giving out wrong signal or ECU screw-up and over-advancing ignition timing that will cause rough running at low RPMS, smoothing out when RPM go up.

Hey Kebowers,

Thanks for your input.
I have checked against the fuel pressure at idle and it was high enough so I dont think the fuel injectors are the issue.
The issue happened suddenly, I just started her up one day and boom, shes shaking like a tractor.
I wouldnt know which cylinders are misfiring since Im not getting any codes at all regarding misfires. I guess its too small of a error to catch?

I also had a thought about it being lean misfires as well but adjusting that didnt make much of a difference in the idle. So O2 sensor outputs are proper.

As for the crankshaft sensor, wouldnt my car be unable to even turn over if the sensor was no good, or at least throw a code? Itll start no problem even after I have it sitting for days.

I think my next step is to replace the coils with brand new ones (Instead of the used ones I replaced it with from a S430 that ran perfectly). And if that doesnt work, I will check all of the electrical connectors that involve the intake manifold since I may have clipped/bent a connector when replacing it. (who knows) Those clips and connectors are pretty fragile from being exposed to so much engine heat after so many years.

When it runs rough use a laser temp gun on exhaust ports to find cold one... that will be the one with misfire... you can then start swapping parts with good cylinder to find out what it is.
if more then one mis fire by having similar temps then you are looking for common air/spark/fuel faults which could be - common sensor issue (Crank, MAF TPS etc) or intake air leak or fuel issue etc.

Might be time to Hook it up to a fancy computer and watch all sensors etc to see what is happening...

You have to reset the adaptations when you do any changes like MAF, O2 sensors, injectors, or even just cleaning the throttle body.

It could also be a throttle body valve is kaput, but before doing any of that, reset the adaptations with an SDS computer.

Check EGR Valve or circuit and there's also a MAP sensor in the front area of the engine that has a hose which if cracked, can cause erroneous readings of actual MAP to the ECU which will throw off the mixture and produce a rough idle. My EGR valve was stuck OPEN not closed like happens most of the time. Here's a youtube video that shows the MAP sensor hose I'm referring to...


Good Luck!