does any one here have experiencing jerking with the engine is cold? I mean sometimes when I drive my car 95 S320 if the temp gauge is under 85C. The car will jerk. The rpm is going down then up again and then down. But this will not happen when the car is warm. Yesterday when I drive up a hill (engine temp 75C) at 3rd gear around 2500rpm. It suddenly the rpm goes down to 700rpm and no throttle response. I have to back off the throttle and hit it again and the power comes back.

Any ideas??

My dealer can not found any fault about it. (I guess it happens for 6 months now) But it is not always there.

 

A dirty fuel filter or bad fuel with water? I would take it to a MB guy to take a look.

 

I already took it to MB for a look but they do not have a clue why it happens. I have changed the oil and oil filter, new spark plugs, new air filter. And the dealer changed the 'electronic throttle' parts but still can't solve it.

Any suggestions?

 

It will only happens sometimes and when it happens, the engine is still cold and below 85C. Never happens when the engine is warm (driven for around 3 miles)

 

Next thing I would check is the oxygen sensor. But I am no MB mechanic.

 

Water temperature sensor may not be working so you are not getting a rich enough mixture when the engine is cold.

barry

 

Thanks for the help. Will check it with my garage. Meanwhile, do you have any more ideas of what others may caused this problem also? My garage can not fix it for 6 months now!

 

Step # 1:

Find a new Garage.

Then have the new garage check the codes.
They have to know that all the sensors are working properly before they start spending your money.


Barry

 

I have the same problem but to my opinion it must be the oxygen sensors since I checked the codes and it gives me the code for oxygen sensor.

 

Step #1 Keep the RPM under 2000 until the engine warms up.
The most wear and tear is exacted on the engine when it is cold.
( In Canada it is a habit to "warm up the car" )

 

did you check your mas sensor?
find a obd2 scanner and hook it up and see what it tells you

 

Thanks for your input. My garage had check my car with the computer but they find NO fault.

Still, my car is still jerking sometimes. driving me crazy!

 

Have you clean your K&N air filter before? I don't have them on my W140, but I have one in my W126, I clean it every 10,000 miles just to keep thing going.

 

The K&N filter is new (about 1000km)

So it's still very fresh

Still no idea why the car sometimes jerk.

 

Do you go to the same gas station to buy gas? If so, I would switch to another to see if the gasoline is low quality or what. Wait until you finish the current tank, go to another place to fill up. Good luck.

 

I always go to different gas station but still problem exists.

I just don't understand why it is so difficult to fix it since I think it is a minor problem.

Getting very depressed!

 

The only reason I could think of why the car 'cough' is either not getting enough gas or air. Now, check your plugs cables. Or it might be a dirty spark plug. Hope this help. I noticed your location is in Hong Kong. Well, the mechanics in Hong Kong are more of less of a grease monkeys IMO.

 

Thanks I really appreciate your help here. The spark plugs have been changed.

I guess it is something rely to the gas-air ratio when the engine is still "cold" Do you have any idea of which part should I look at since I am not a mechanic.

Thanks again

 

What about the distributor? Check that too. When things are cold, you feel the jerking, and when things heat up, it's gone. Let me ask my MB guy next week and get back to you. He has a 420SEL and he takes care of his customers' as his own.

 

dtkw,

Thanks alot for your kind help. you are a good man!

By the way, my car is 1995 S320 long wheel base model.

When engine is cold, sometimes it will jerk (rpm drop for a second, then come back and drop and come back. You get the picture. Once the engine is warm (driven for around 3 miles and engine temp reaches more than 85C. It will not happen.

Thanks again

 

Now I see the logic. Jerking when cold because the combustions ain't enough to push everything into motion smoothly. I definately think either one of your spark plugs weren't put in corrrectly. Or a fault at the distributor. When the engine is warm, the other spark plugs and the engine developed enough heat for most part so you don't feel the jerking. Good luck anyway. BTW, no need to get depress over a car, a hot chick? sure, but not a car.

 

But the spark plugs are new. What is the "distributor"?? Do you mean the fuel distributor?

 

New? Doesn't matter if they are not gapped correctly. And I hope you are not using those fancy plus 4 stuffs. The distributor is the unit where all your spark plug cables connected to get electric to fire the spart plugs. Good luck.

 

RD Sport, any update on your problem? Fixed?

 

dtkw, thanks alot for asking.

No, still the same. I am planning to leave it like that.

But in the past 4 days, it does not have the problem but this morning, the car jerked 3 times.

It's ridiculous! Driving an S class with the car jerking, can you imagine how I feel?