my 2002passat engine shakes when in idle or stop at light. when running on highway, it is smooth. what could it be?
There could be a number of causes. If the car is in gear and your foot on the brake, you need an idle adjustment.
If the car has air conditioning, look for a dragging compressor putting too much load on the idling engine. We had a Ford which would just stall, and the compressor was in process of seizing up.
Take it to a good mechanic; you don’t need the dealer to try to diagnose this.
Automatic or manual? If auto which automatic? Gasoline or diesel?
Does it stop shaking if you give it a little fuel, but keep your foot on the brake?
If gasoline, when was the last time the plugs and wires replaced? Does it have a CEL (Check Engine Light)? If so get the code read. Many auto part stores will check that for free. That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.
Is the check engine light on or off?
Does your car do this in Park or neutral?