1999 Audi Quattro Hard time re-starting after engine has be

Strange problem. My car starts without a problem when the car is cold, but if it's been running for a little while (usually more than 30 minutes) and the engine is warmed up, it has a hard time restarting after I turn off the engine (stopping at a gas station is always a hassle).

The engine eventually catches (very slow, gradual catch), but it just cranks and cranks and cranks sometimes for 15-20 seconds before that happens.

Any ideas?

Audi A4 Quattro 1.8T