Volkswagen: 1992 Passat engine idle, oxygen sensor, motor mounts

Question
John: I have a 1992 Passat 2.0L 16V 4cyl auto trans 65K mi. The engine vibrates excessively at idle only when in gear, worse when the AC is on. Idle speed in gear is about 750 rpm. Motor mounts were replaced with no change in problem. I changed plugs, wires, cap, rotor. Just replaced catalytic conv. I read that it could be the oxygen sensor and/or the coolant sensor. If so where are they and can I replace either myself? Thanks.

Answer
the temperature sensor is in the coolant flange somewhere on the cylinder head, it should be either a two pin blue one or a 4 pin square one. the lambda probe is in the exhaust system, probably just in front of the catalytic converter underneath the car. both are fairly easy to replace. i would advise starting with the temp sensor.