I'm having a problem with my 96 Jetta GLX (VR6). The idle will "bounce" between 500 and 600 rpm. The weird thing about this is that it only happens when the car is moving. As soon as I come to a complete stop. The idle jumps to 700 rpm and stablizes. I've had this problem for a couple of years now and it seems to be getting worse. The parts that have recently been changed (so aren't the problem) are hose between the throtle-body and the MAS, spark plugs, ignition wires, coil, MAS and both O2 sensors. Anyone have any ideas?