2001 Mitsubishi Galant Timing Belt problem

Hi paul64. Welcome to the forum. Your logic about the motor mounts makes sense except for the fact that one probably had to be removed to replace the timing belt. One of the three mounts will set the position of the engine. If the removed mount wasn't reinstalled in exactly the same spot, one of them could be rubbing metal on metal. That will transfer normal engine vibration to the frame of the car. All of the mounts have rubber isolators between the metal brackets but typically two of them can slide freely. They are centered by the one stationary mount or by repositioning one of their brackets. Mounts are especially suspect because you noticed the engine seems to have normal power, and the vibration changes with changes in torque on the engine.

Some engines use a "balance shaft" that is run by the timing belt. When it is not timed correctly, you will feel a miserable vibration, but it gets worse at higher engine speeds. That doesn't agree with your observations.

Caradiodoc

Rather than run from shop to shop, go back to the one that did the work and give them a chance to find the problem. If they are a reputable shop they will want to make it right and learn from their mistake. Any other shop will start from scratch and look for the cause of the problem without the benefit of being involved in the previous recent history of the car. It's like running from doctor to doctor when the first one doesn't cure you on the first visit. Each one will start fresh and you'll never get past the first round of tests.

The throttle position sensor tells the Engine Computer how far you have the accelerator pedal pushed, which way it is moving, how fast, and when it is at idle or wide-open-throttle. That has nothing to do with a vibration. The same is true of the air intake duct work unless something is mispositioned and rubbing, but I don't think you would feel that as a vibration.

Caradiodoc

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.

Caradiodoc