If I start it and keep it above 1500 rpm's it is fine but if it falls below 1500 rpm's it won't rev again just idles rough. Changed plugs and wires. Took air filter housing loose, and it revs when fuel is dribbled in air breather. Changed fuel filter about 6 months ago.

 

look for a vacuum leak.

 

Is there a problem checking fuel pressure with a gauge?
A problem looking for codes with a reader or scanner?

 

Would you believe a mouse got into the air filter and chewed it up and a piece of paper got caught in the mass air flow sensor. Took it out and it runs fine.