90 lx 5.0 convrt wont start

Have a 90 lx 5.0 cnvrt that runs fine some days on others it will not start (backfires acts like not getting fuel) will seem to start while key is cranking but falls dead when key released to run position. Also dies when cold at idle around 650 rpm any info would be greatly appreciated.

OK have replaced the plugs wires fuel filter air filter and disconnected battery for 1 hour. still no start. still acts like something electronic as it started fine and ran fine thru a 75 mile cruise on sat. after noon. Thinking maybe ign. coil or ign. switch seems to fire ok and run sort of while the key is in the start position but wont stay running when key is released. please help!

i would try swapping out the ignition key and see what happens. or if you have the schematic for the car you can jump it to the on position and see what it does.

problem solved it was the ignition module had gone bad thanks all