Symptom: When I drive the car between 30-40 MPH (2,000 RPM) and then come to a stop at a light or whatever idling, OR idle the car stationary at around 2,000 RPM, as soon as I completely let off the accelerator and the engine returns to idle the car shakes very noticeably for about 5 seconds and then gradually smooths out. This started about a month ago and the car ('84 300D) has about 120,000mi.
I've replaced both fuel filters and the symptom hasn't gone away. The shaking happens in all gears (I haven't tried reverse at 30-40!) Could this be that the fuel pump is showing signs of failure? Is there some sort of idle adjustment that could be stuck? What would cause shaking and then the problem smoothing out on its own?
Would appreciate help.