There are about three places for fuel pressure to leak away, assuming you don't see external fuel leaks. Check valve in fuel pump , requlator, one of the injectors.

Since you say the problem is worse when hot it seems like the issue is "too rich". One or more injectors could be not sealing tight which would allow fuel to leak into the intake manifold. If a diaphram in the pressure regulator is leaking I would think you could smell gas if you pull the manifold vacuum hose from the requlator off.

When the car does start, does the exhaust smell "gassy"?

There is a check valve in the fuel pump which is supposed to hold pressure when the pump shuts down. The control system only lets the pump run for a second or so when you turn the key until the engine starts. If your check valve is dumping the fuel pressure quickly, try moving the key quickly from off to start to see if you can get it cranking before the pressure goes away.

--
'96 965 with 16' wheels at 103K. Had '85 745 Turbo Diesel for 200K.

I would suspect the fuel pressure regulator. They can leak internally and send fuel into the intake manifold which causes a rich condition which makes hot starts difficult.

It is located just forward of the fire wall, on the intake side, near the vacuum valve for the cruise control, it is a small silvery cylinder with one vacuum hose connected and two fuel lines.

Another cause may be the temperature sending unit to the ECM, not the one for the dash guage. Could be always sending the signal that the engine is not warm and making the engine rich.

Are there any codes stored?

DanR 94 964 223,000 miles
--
DanR