1991 DX
It will turn over, but not start. After checking spark and fuel I went to the air filter. Took the old one out - car started fine. Put new filter in - car will not start.

What would cause it to only run without a filter?

 

not really sure about the filter thing but ive recently been having trouble w/ my car starting too. when you put it in the on position listen to see if the fuel pump is coming on, my pump wasnt coming on so obviously my car didn't start...after a couple minutes it kicked on and ran fine, it was a problem with the main relay.

 

Try to take the airbox out and the plumbing that goes to the throttle body. Clean all of it out and reassemble with the new filter. I'm thinking that there is a restriction in the engine somewhere and the air filter + resistance is chocking the engine. Take out the air filter and you only have the resistance so there is some air reaching the engine.

 

sounds like a throttle body problem, unless it was just a coincidence