Starting problem when warm
 

My 88 325ic normally runs great, loves to cruise the mountains between 80 and 100 mph. I can reach in and turn the key and it starts great when it is cold, and 19 out of 20 times when hot.
But that 1 in 20 is when it has been off for about 5 minutes. To start it that time I have to push the accelerator to the floor and hold it there. After turning over a while it starts. If I just let it sit an extra 5 minutes, it starts without the accelerator.

Plugs, wires, mass flow meter, hoses, thermostat are all less than 8,000 miles. No difference whether I mix 50% aviation gas or only 20%, but I normally run about 30%. (No premium in town, only 80 octane regular)

Only has about 130,000 miles on it.

No thoughts on the cause?