Hey mike this sounds like a couple of things here one or the other so lets go around the car and check each one if there's to much dielectric grease on the plug boots it's melting and bridging the spark from the plug + with the - head and the boots will be mushy/soft I'm going here because you say that when it heats up this starts take of the wires one at a time and check for this also take out each plug and check for antifreeze there could be a leak and it's running into the cylinder by the way what motor is this? also if you find this there it could be a cracked head if no signs of this are present next go to the distributor check the rotor and cap for wear and remember this car is 21 years old now it came out in fall of 94 the pick-up coil in the distributor has probably seen better days as long as this is the 5.0/5.8 motor if it's the 6 check the coil pack where the plug connects it could be cracked there at the back part where it comes from the female plug in part and expands when it gets hot from repeated firing then the voltage escapes check all connections for the ignition the high idle part is related to possible low antifreeze or the computer is trying to correct the misfire by raising the idle post back with progress and engine size and any modifications that are not stock to the vehicle stephen