84 300D Sedan

Hi everyone,

I need some help on trouble shooting a sticking accelerator. Today when I was driving from work I exited the fwy and shortly after, the accelerator pedal got stuck and dangerously began accelerating the car in a residential neighborhood. The problem went away as fast as it came. I thought it might have been my mat stuck on the pedal, or my work shoes. Later in the evening, I drove out again and to my shock the car ran away again, with a motorcycle cop right behind me. The speed quickly picked up to 70-80-90 etc. and I'm standing on the brakes and trying to steer off the road. I come to a stop and pop the car into Park and the RPM's are now off the Tach (over 6000). Very scary stuff.

Good thing these are some slow cars because he didn't notice a thing. Any ideas what might be causing this? I don't want to take apart the throttle linkages unless I really have to. I am reluctant to drive it now because who knows when it will run away again. Please help.
Thanks!

Next time when it happens put the car in neutral or turn the engine off. It might save your life.

Not sure about the w123 but on a late model w126 you can turn the key all the way off and it wont lock the steering until you pull out the key

Are you sure you are not experiencing the pre-cursor to a true runaway? First thing I would do is check the oil level and see if you have lost a noticeable amount of oil which would mean the engine is ingesting the motor oil and burning it as fuel. Then I would pull the air cleaner and see if it is got any significant amounts of oil it in. I would also see if there is oil in the black plastic elbow going to the turbo. You could have a significant amount of blow-by causing the engine to runaway on engine oil. OR the turbo seal could have failed allowing oil into the intake causing uncontrolled engine acceleration.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

I just looked up what a runaway diesel is boy that is frightening. I have alot or blobby in the engine and a moderate amount of oil in the air filter. Would the emergency shutoff valve still work in an event of of a run away diesel because when this happened to me the shutoff valve worked just fine for me.

In a true runaway I highly doubt that the shutoff lever would stop it as that is only used to cut off the fuel supply coming from the injection pump. In a runaway the engine is using its own oil as fuel, and since there is no way to control the amount of oil it is sucking up, there is no way to control it. I have heard a runaway can be stopped by cutting off the air flow using a piece of 3/4 or 1 inch plywood over the air intake on the air filter housing, but I really would not want to be that close to a screaming diesel running at over 6000 RPM.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Have you get a cruse control on your car that just might be in the engaged mode ? .

I really think it might just be CC randomly kicking on, because it only happens after like 5mins of driving. If were to disable it can I just remove the linkage connected to it?

Yes it could possibly be cruise control. You can disconnect the linkage and it will no longer function. Or you can unplug the connector going to it and disable it that way.......or you can do both. Hopefully that is all it is, but be prepared just in case it takes off on you again.......

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Had you done an work under the hood lately?

Spray down all of the Linkages ball areas with WD-40. It is not a great lube but if the sticking goes away you know where the issue is.

Inspect all of the under that hood linkages with special attention to the pivot on the fire wall.

There is a throttle return spring under the Fuel Injection Pump and maybe another one near the fire wall (memory is not clear on that one).

Pull out your mats and inspect all of the pedal linkages inside of the car and where the pedal bolts down to the floor.

I don't know why it would suddenly cause an issue but if your Rack Damper/Governor Idle Pin is in to far it is said it can run away like that (the idel speed is not supposed to be adjusted with that part). Back it out and if that issue goes away that is the problem.
If that turns out to be the issue use the nrmal idle adjusment screw on the Engine side of the Fuel Injection Pump and then slowly turn in the Rack Damper/Governor Idle Pin till you have removed the idle shaking without increasing the idle speed.

Take a picture of the Cruise Control linkages and disconnect them from the Throttle linkages and wire them out of the way to see if that is the issue.

The only other way I can think of that your Engine could get something to run on is if your Turbo compressor side was leaking oil into the Intake or a whole lot of oil would some how have to go by your intake valves and down into the cylinder.

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84 300D, 82 Volvo 244Gl Diesel

I'm thinking that you mean cutting off the main air supply source/intake at the turbo charger (attached picture), not the small tube at the top of the valve cover.

Attached Thumbnails

 

check the plastic piece on top of the valve cover the cam that controls the plastic
valve get hung in the open position due to wear in the plastic.

of course that this opportunity to lube ALL the pivots points.

Check the oil level. Fuel getting in could raise the level far to high. Just something to quickly check. Not expected to be the issue.