i have a 93 maxima and im having some problems now in december of 2006 i had put in a used engine because i blew the timing belt so i replaced the engine,i drove it for a month and let it sit for a few weeks ,now all of a sudden when i start the car it idle's fine as soon as i put my foot on the padal the engine shakes and there is a taping noise ,i did replace the plugs and wires on the newer engine but it didnt fix it SOMEONE PLEASE POINT ME IN THE RIGHT DIRECTION, now for some reason im thinking the MAS ? i dont know

 

If the timing belt broke it is very possible you bent a valve.

 

Your second engine belt is/has been always ok, I guess?

 

MAF is one of the possibilities. Disconnect it and test: youll have 2.2k rpm ceiling and different beahviour. Then measure MAF signal linear voltage level output; clic link below and check page9.

The Nissan 6cyl caps are problematic, do check twice. Check also distr grounding...