Hi all, nice to be back to this board, om606 newbie with an idle problem. Its a 1999 e300 turbo diesel with 198k mi and when its starts up in the morning it runs smooth at idle, even after a few runs around the block after the engine has come up to normal operating temp it still runs fine but after a long drive on the highway and you come to a red light the engine starts to rock from side to side as if it was running on 4 cylinders and the whole car rocks, this is more pronounced when the brake pedal is pressed. I tried adjusting the cable that operates the accel position sensor but this only makes it run at higher speed when the car is cold but when is hot it runs bad. The car runs like a rocket otherwise, where should I start?

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87 300d Turbo 241K with original #14 head (blue)
87 300d Turbo 198K will run great again someday (silver)
84 300sd sold ( buyer drove it to Paraguay )