I've never actually driven a car on the road with a mistimed balance shaft but from what people have told me, it's no fun. It's only purpose is to counteract normal engine pulsations which are more noticeable in four cylinder engines. A few six cylinder engines use them too. When they are out of time, even by a little bit, their vibrations add to and multiply engine vibration. You'll feel it in the steering wheel and seat. You will also feel an unusual amount of vibration by just holding your hand on the engine. If you do not, then I would continue looking for something rubbing that is transferring engine vibration to the passenger compartment. Start by looking at things that were disturbed, moved, repositioned, or removed and reinstalled when the timing belt was replaced.
Other common items that cause this are exhaust system hangers where the two parts of the metal brackets are touching each other, a binding flexible exhaust joint at the rear of the engine, and anything on the engine that is rubbing against the body.
You might also listen by the tail pipe for an unusual putt - putt sound when the engine is idling. That would be a sign of a bent valve. On some engines, improper procedures during the timing belt replacement can cause some of the valves to be damaged. Really serious damage will occur on those engines if the timing belt breaks while driving. I suspect that is not the problem because what you're describing sounds like a higher frequency vibration. A bad valve will still allow the engine to build normal power, but you will feel the vibration as about two thumps per second at idle.
Thursday, October 28th, 2010 AT 8:18 PM