1996 Mercedes E280, inline 6 M104 engine RPM bouncing up and down/stalling during city driving

[M104]

Hi everyone,

I've had this issue for almost two years now. The problem occurs during city driving and traffic when i have to lightly press the gas pedal or the brake pedal one after the other or when coasting at low speed after ligthly pressing the gas pedal.

RPM keeps boucing up and down at a 1 sec interval and makes the whole car jerk forward for a few sec before idle settles back to normal again. I used to make it stall a lot by pressing the gas at the wrong moment when rpm is at the lowest but got used to it and somehow manage to it drive normally. My wife drove the car and thought it was undriveable.

Otherwise it starts and drives perfectly but sometimes i look at the tach and rpm seems to fluctuate very slightly under load in high gear and low rpm but it is barely noticeable.

Things i've checked and other useful information :

- No vacuum leak that i can find using various methods.
- Throttle body cleaned.
- MAF Cleaned.
- Never had a DTC.
- New fuel filter.
- Spark plugs replaced slightly over a year ago by the correct Beru reference as written under the hood.
- Original coils and wires.
- Normal fuel consumption.
- Purge valve is not stuck open (but i've heard it clicking).
- Problem might be slightly worse after a hot start or during hot weather.
- Problem almost non existant when pressing the gas pedal in park.
- I can replicate the problem with the car stopped if i quickly tap the gas pedal in drive with the other foot on the brake.
- This car doesn't have an idle control valve, idle regulation is done by the ECU and the throttle plate.
- The gas pedal cable is not too tight.

Car is a 96 Mercedes E280, inline 6 M104 engine, 722.5 transmission, 165 000 km (100 000 miles).

I'm really scratching my head with this one!

 

[GMBoy]

This sounds like a transmission issue especially since it does it in drive but not park. Check the torque converter function...I would do a fluid service and see if that cures it or helps if you have not done it over the last 30-50k miles.

 

[Kestas]

Have you replaced the engine wiring harness and throttle body wiring? I did that on my M104 95 E320. No mechanic will work on driveability issues on this model unless the wiring is replaced. For three years Mercedes made wiring from earth friendly insulating material that decomposes in the landfill. Unfortunately, the wiring decomposes while the car is in service. Take a peek under the wrapping.

 

[M104]

Forgot about this, my car doesn't have the eco junk wiring harness. W210s weren't affected. I had to rebuild it on the previous 93 and 95 W124s i owned.

Transmission has been serviced every 30 to 50k km from new and is in perfect shape. I said that the problem doesn't occur in park but if it starts bouncing, i can throw it in neutral or park quickly and it will continue for a few second.

 

[M104]

I am not a fan of throwing parts at a problem but i have no way of knowing live data while the problem occurs and am tempted to replace the MAF. I've heard that it is short lived on this engine because it sits right above the exhaust manifolds.

 

[jmanbball]

I'm pretty sure that early 1996 W210's could have wiring insulation issues too, so I'd double check the wiring. Sounds like a throttle body issue to me. While not necessarily worn out, it is getting old too. I would look on ebay for one with a 2000+ date code. I just replaced it on the 1995 W124 I had already replaced the wiring on.

 

[mk378]

- No vacuum leak that i can find using various methods.

You also need to check between the MAF and the throttle body and the PCV system. Air leaks anywhere after the MAF will cause idling problems.
Note that a vacuum brake booster lets a lot of unmetered air into the engine to recharge as the brake pedal is released. This usually isn't a problem because the driver typically mashes the gas pedal at that time.

 

[Trav]

Have you replaced the engine wiring harness and throttle body wiring? I did that on my M104 95 E320. No mechanic will work on driveability issues on this model unless the wiring is replaced. For three years Mercedes made wiring from earth friendly insulating material that decomposes in the landfill. Unfortunately, the wiring decomposes while the car is in service. Take a peek under the wrapping.

View attachment 336206
View attachment 336205

Soy based insulation?

 

[bladecutter]

Hi everyone,

I've had this issue for almost two years now. The problem occurs during city driving and traffic when i have to lightly press the gas pedal or the brake pedal one after the other or when coasting at low speed after ligthly pressing the gas pedal.

RPM keeps boucing up and down at a 1 sec interval and makes the whole car jerk forward for a few sec before idle settles back to normal again. I used to make it stall a lot by pressing the gas at the wrong moment when rpm is at the lowest but got used to it and somehow manage to it drive normally. My wife drove the car and thought it was undriveable.

Otherwise it starts and drives perfectly but sometimes i look at the tach and rpm seems to fluctuate very slightly under load in high gear and low rpm but it is barely noticeable.

Things i've checked and other useful information :


- Original coils and wires.
- Problem might be slightly worse after a hot start or during hot weather.

Might be worth replacing those original wires from 1996.
Also, when is the last time the valves were adjusted on this engine?

 

[CleanSump]

Soy based insulation?

Yes. It was a headache for many who bought '90s MBs. Early breaking and cracking shorts, mice eating the insulation,.... Wasn't a problem on my '92.

 

[jmanbball]

Might be worth replacing those original wires from 1996.
Also, when is the last time the valves were adjusted on this engine?

They have hydraulic lifters, so no adjustment.

 

[M104]

I'm pretty sure that early 1996 W210's could have wiring insulation issues too, so I'd double check the wiring. Sounds like a throttle body issue to me. While not necessarily worn out, it is getting old too. I would look on ebay for one with a 2000+ date code. I just replaced it on the 1995 W124 I had already replaced the wiring on.

100% sure it doesn't have the bad wiring harness, i've checked, all wires are like new and insulation is not made from the same material as the wiring found in W124s. However i can't be sure about the throttle body but i've heard from various sources that W210s weren't affected and as far as i'm concerned i've never seen the problem occur a 210.

For what it is worth, i have cleaned the throttle body as best as i could and decided to remove a fuel hose that looked like it had a slight kink to find this. The fuel rail has it's own tiny filter like a fuel injector! I could barely blow through it. I just drilled the thing out as i don't think it is really needed. Fuel pressure was certainly correct as i didn't have any lean codes or performance issue but maybe it was slow to adjust at times, i don't know.

It feels like either cleaning the throttle body or removing this filter helped mitigate the issue but i have to drive the car more. Maybe just removing the pipe between the MAF and the throttle body and tightening it again.

 

[Boomer]

If the fuel rail filter had so much crud that you could hardly blow through it, you are now letting that stuff go to your injectors. You might be wise to replace the part rather than running an ol older one that you have drilled out. Just a thought.

 

[M104]

The filter is so fine that it was clogged with almost nothing. The fuel system in this car is really clean and i believe that the main fuel filter combined with the little filter on the injectors are enough on any vehicle. This is some Mercedes over engineering in my opinion. I like to remove the injectors as routine maintenance every few years and replace the filters if they are dirty anyway.