I have an 83, V8 5.0 Thunderbird with 140,000 miles.

If I have my car sitting around for 1-3 hours and try and start it,
occasionally it will not start.

However when it starts, in park the engine will run fine for around 5
minutes then will start to repeatedly choke, run, and eventually will
die unless I hit the gas. Now if I try and drive the car I can back up
fine yet as soon as I shift to drive and hit the gas the engine will
shutter or will die if I press the gas too much but if I barely press
the gas I can drive fine.

When testing for a spark I turn the key and get a brief spark. The
spark then disappears as I continue to crank the engine. I've adjusted
the spark gap at various settings but there is no change in the spark.

This problem has started to happen more often lately. In the past when
my car would die out during driving I could jump out the car and would
get full spark when cranking the engine and engine would start right
up with no hesitation.

I've had the ignition coil, ignition modulator, and distributor cap
replaced. It is not in need of a tune up; I have checked the spark
plugs and plug wires. I have also checked the wiring from the ignition
coil to the ign. modulator to see if ripped etc., there was some
fraying on some wires so I repaired as required.

If anyone has some ideas on this I'd appreciate any information. Also
I have all maintenance records from 140,000 miles to 80,000.