Dear all,

I am new to this fantastic forum. I have been a w124 fan for many years and have had a quite a few of them in different versions. I have been reading diverse articles and threads on here for the past 3 months and I am impressed with the knowledge of its members. It so happens that I have now a very well maintained and relatively low mileage 300TE-24 1990 model. 208.000 km. on the clock. I absolutely love this car but it is driving me to the brink of nervous breakdown. For the whole summer I have been working on a few issues related to accelerator hesitation, fluttering and sputtering with almost no luck.

But here goes,

Description of problems:

1. Sometimes the car runs and drives absolutely fine. There has always been an issue with starting and full throttle though. When I floor it and push the kick down switch it takes off like an airplane but at some point during the acceleration (not always at the same point and not always the same intensity) the car hesitates badly until I release the gas pedal a little (again different how much from time to time). It sounds and feels like it is choking when this happens.

2. The idle has been steady at 700 rpm most of the time but after full throttle driving (I take care of my w124s so alot of full throttle is not something my cars are used to) the idle jumps up to around 1500 rpms and then fluctuates from around 1000 to 1500 rpms. It does not come back down to 700. But if I turn the car off and on again everything is fine.

3. I have always had problems with starting the car. Usually I start it and it instantly dies on me. Usually it takes one to two more starts to get it going and I am used to "catching" it on the start. Pressing the gas pedal a little to get it going.

4. Like stated before, the car can sometimes drive absolutely fine (not counting the starting and full throttle issue which are always there). It can be fine for a couple of weeks and then POW! Sputters at different levels of the gas pedal pressing. I can usually find a spot on the gas pedal where it goes fine but its a delicate process. This is worst then I am taking off or accelerating to overtake cars and such. It seems that this is worse when there is not much gas left in the tank but I cant be absolutely sure. It can happen also with a full tank of gas.

Things I have done so far:

1. New OVP Relay (ofcourse
2. New Recomended High Quality Bosch spark plug wires
3. New Recommended spark plugs
4. New Recommended Bosch Rotor arm and distributor cap
5. Replaced the fuel divider (with a used one
6. New o2 sensor
7. New Crankshaft sensor
8. Checked vacuum lines for leaks
9. Adjusted the Duty cycle to optimal setting
10. One of the fuel pumps replaced

Things I have not yet tested or done (please comment if any of these could cause this behavior in your opinion):

1. fuel pump relay
2. throttle pos sensor
3. camshaft sensor
4. fuel pressure regulator
5. temp sensor
6. Fuel filter

I would really appreciate it if someone could comment on this if they see a pattern that leads to something I am missing here or if someone has been in this mess like me.

thank you

 

ecu temp sensor

 

Just replaced temp sensor,

Started with half a turn, ran absolutely great, took it to the freeway and it ran like a rocket with no hesitation. A big smile on my face.

15 minutes later... same story.... all the symptoms back I could'nt believe it.

I wonder why it was ok for a short period of time??

 

Dang it. The symptoms matched.
I'm clueless then, but it has to do with an intermittent sensor.
Check the throttle position sensor?

Ever pull heavy current off the cigarette lighter? That's been known to affect the ecu.

There is a pin combination that powers the fuel pump without relay, as in when symptoms appear, pull the relay and link the pins.

 

I am no expert on the w124, but there are some things that are common to most cars. Fuel filter, fuel pump, crank position sensor are areas that cause the problems you describe in any modern car.

Then specific to these cars is the bad wire harness situation, which requires replacement.

 

Ptoro1: There are aparently two temp sensors. 2 pin and 4 pin. I replaced the 2 pin. should I replace the other one as well? I replaced the throttle positioning sensor and it seems that the car fires up much better but now its running around 1000 to 1400 rpms idle?? weird

This car does not have the fuel pump relays, instead it has the MAS module. I think there is info on here somewhere how to link the pins on it. I will have a look at it.

XJguy: Thank you for the input. All the mentioned items have been replaced with limited luck unfortunately. I will be starting a fuel pressure test soon, regulator, accumulator and such

 

You replaced the sensor for the instrument cluster display. A big yes on the 4 pin one, that's the ecu sensor.

When you replaced the throttle position sensor, you had to remove the fuel distributor from the assembly right? In that case you have to readjust the air fuel screw. Basically, the pin under the flap is the wrong height which is why idle is off.

Oh correct, you have a mas relay. I wouldn't mess with it, those don't fail in the same way. With fuel pumps, they either work or they don't. So if you can hear them "hiss", they're on.