1991 300D - intermittent rough idle

[Chris_]

Hello.

My 1991 300D 2.5 is providing an intermittent rough idle...here is the detail of symptom.
1) Just before coming to a complete stop ( on braking gently) there is a discernible vibration which feels like a cylinder miss.

2) at a complete stop in drive... the car will vibrate which also feels like a miss however if while holding the brake I lightly spike the throttle and allow the engine to drop right back to idle the "miss" will either dissipate or completely disappear until the next time I come to a stop

3) To clarify ..the "miss" is not always present and varies in intensity and is only discernible at idle

4) furthermore the car runs very well down the highway and at intermediate speeds with as much or possibly more power than normal..in addition when accelerating from a dead stop with or without the miss present it accelerates very acceptably ( fuel mileage is good )

* the car has 188K on it and has had a headgasket at 150K and a timing chain at 174K both of which I have done myself

A) Is this possibly an injector ?

B) Could this be a fuel quality issue or could it be related to the injection system/pump

any thoughts appreciated...Thanks
Chris