Volkswagen Repair: Idle, fuel delivery system, fuel system cleaners

Question
I have an 87 Fox wagon. It runs Very rough and never even.. I have to adjust it constantly. and never really get it right. Now it has this new thing.... Going down the road it feels like some one is hitting the brake . It doesn't feel like the engine.. but I have no clue .This is something just started. I am thinking... maybe a sensor? that cuts in and out ? Any clues? It is a standard transmission.

appreciate any Ideas.
Thanx. G

Answer
Hi Georgia;
I can't say for certain, but the symptoms sound like a fuel problem, and the "bucking" is a cylinder not quite full enough, or too full of fuel and air that delays it's ignition...is this car a diesel?  If diesel, the ignitions would become even more violent, and make the car lurch abruptly.  My biggest question is about the fuel delivery system.  If gasoline, this should be "CIS-e?" I think.  They can become notorious for fuel filter problems, and generate huge fuel pressures.  60-75 psi nominal pressure.  Filters from VW don't pass fuel system cleaners, or water, or most other impurities.  In fact, the pressure can be great enough to make the filter material wad up inside the canister.  A FRAM brand filter is far more forgiving.  Hope this helps, good luck Georgia.