A thumping heard and felt in the floor is often caused by failing engine mounts. A failing mount allows too much movement of the engine, and will require replacement.
2001 Nissan Quest Problem Reports
Newest 2001 Nissan Quest Problem Reports
The distributor shaft bearing can become rusty, and seize causing the engine to stall or not start. The failed distributor will commonly require replacement.
The fuel injectors can fail and cause drivability problems. Often there is no Check Engine light and the failures can be caused by corrosion of the connector, clogging beyond the point of cleaning, and/or internal failures.