81 300sd throttle behaving strangely

[Aponty]

As a quick back story, when driving home recently, I pushed my pedal to accelerate, the engine lurched, then engine speed dropped to idle and a drove home at about 1mph. I found that the endplate on the linkage rod coming from the firewall had come loose and wasnt moving with my pedal. I took it apart, matched up the rotation angle as best I could, and welded it. For 2 weeks now the car has been driving great, but today (very cold day), the throttle has been acting up in a strange way. When in park, if I rev the engine, RPMs drop back to idle quickly as they should when I let off the pedal. When driving, the RPMs return to idle slowly, almost as though the throttle linkage is sticky or poorly lubricated. But it doesnt behave this way when in park! Has anyone experienced this issue or have any thoughts on it?

[evranch]

I would suspect your kickdown cable is gumming up in the cold, and something about the transmission linkage is making it behave differently in P and D.

Also considering it's "very cold", it's possible something (like the kickdown cable) is freezing/gelling up while driving from the cold air flow, but when parked the waste heat from the engine thaws it out. I've seen issues like this here in Canada with older vehicles, particularly Bowden cables for defroster dampers etc.

[Diesel911]

Originally Posted by Aponty

As a quick back story, when driving home recently, I pushed my pedal to accelerate, the engine lurched, then engine speed dropped to idle and a drove home at about 1mph. I found that the endplate on the linkage rod coming from the firewall had come loose and wasnt moving with my pedal. I took it apart, matched up the rotation angle as best I could, and welded it. For 2 weeks now the car has been driving great, but today (very cold day), the throttle has been acting up in a strange way. When in park, if I rev the engine, RPMs drop back to idle quickly as they should when I let off the pedal. When driving, the RPMs return to idle slowly, almost as though the throttle linkage is sticky or poorly lubricated. But it doesnt behave this way when in park! Has anyone experienced this issue or have any thoughts on it?

Not sure if this is what you are speakig of or not: Accelerator Linkage Pivot Mount that is on the fire wall. I am not sure if the one on the SD is the same.


There is a pic of one from a W123 in post 4.
Which part is this?

There are a few things that happen to them. One is the rubber between the parts shears/tears. Behind the metal bracket is a plastic ball that in time simply falls apart. When that ball falls apart the pivot sometimes pulls forward and out of the ball.

I think if the pivot gets loose enough it is possible to lose the accelerator pedal spring which is down under that somewhere.

As best as I can tell yours looks different, but it still has other parts that can deteriorate.