My 85 4000 Quattro recently started bucking when I let off the throttle. It doesnt do it all the time, just occasionally. If I have my foot on the throttle, and then let off completely to start slowing down it will buck slightly, then run fine. It will also do it occasionaly if i am running at a low rpm slightly lugging the engine. Anybody have an ideas of where to start to troubleshoot this?
Thanks

try replacing the fuel filter and cleaning the injectors and lines.

I replaced both fuel filters less than 500 miles ago. Havent run any fuel injector cleaner through it in a while. Maybe ill try that

Try B&G 44K- the stuff works wonders. But make sure you have a full tank of gas when adding or you'll fry your injector seals.

Check the rubber boot leading from the air cleaner to the intake manifold. If it is cracked, there is the possibility that air is getting into the engine that is not being registered by your diaphram that is above the air cleaner. This will affect the air/fuel mixture on the car, and may produce the bucking you mentioned.

-- Tom