Gary's Garage - Throttle Cable

I’m going to cover a trivial issue, though it didn’t seem so trivial when it happened to me while driving the 1992 300CE-24 about 60 in the left lane of I95 through Jacksonville. I felt a thunk in the throttle and then suddenly had no throttle control. The engine went to idle and stayed there no matter what I did with the gas pedal. I was able to get into the emergency lane on the Trout River bridge and since the engine was at idle, I was able to continue to a safer position on one of the exits.

Since I felt it in my accelerator pedal, I thought that I’d either broken the accelerator cable or the cable end had popped off. I was very fortunate to find that I did have a Mercedes tool kit in the car. With Cheryl warning traffic away from me, I got on my knees and pulled the panel around the pedals so I could see the accelerator pedal end of the cable and found that it was fully attached. I then moved to the engine compartment; I had to remove the air cleaner so I could see the other end of the cable.

By this time, two guys in a pickup enroute to the pull a part pulled over to offer help, not that they’ve ever seen a Mercedes straight six before, but I had gotten to the engine end of the accelerate cable, and I could see that the cable had pulled through its bracket. There was nothing visible to attach the end of the cable to the bracket. The guys that pulled over were kind enough to let me have some tie wraps, and I was able to tie wrap the end of the cable into the bracket which allowed me to again control the throttle with the accelerator pedal. I put things back together and we were able to continue home, though with a higher idle since the cable adjustment wasn’t correct.

Once I arrived home, I found that there is a $2.79 part called a throttle cable guide which sits within the metal bracket and there is a round part on the cable that seats in this throttle cable guide. This throttle cable guide transfers the pulling motion of the cable to the bracket which through a complex linkage, pulls the throttle open. With time the plastic throttle cable guide gets brittle, breaks and disappears, allowing the round piece on the cable to pull straight through the bracket without moving it a bit.

I went out to my parts car, located the missing part, removed it and as I was attempting to install it, I dropped it and it disappeared into the engine compartment. I then went inside and ordered a new part. While ordering it I was surprised to find out that this part is common to most of the later W124 chassis with gasoline engines - I have six cars that use this part, so I ordered six of them and plan to put one in each of the tool kits.

If I didn’t have a tool kit, I would not have been able to affect this roadside repair. Even without the tie wrap from the good Samaritan I probably would’ve figured out some way of jury rigging the throttle cable linkage, but I could not have removed the air filter without the tool kit. The tie wraps did make it easier, and I think I will keep some in the tool kit as well. If you have a late 124, I suggest either replace the throttle cable guide or get a few of them and carry them in your tool kit. And check that your Mercedes has its factory tool kit – they tend to disappear as the cars change hands. I have bought cars that did not have tool kits and have successfully found replacement tool kits on ebay. Fixing this alongside the rode beats getting towed home any day.