(I have a 2003 Z4, but..)
From http://www.autoblog.com/buy/2004-BMW-Z4/recalls/:
NHTSA CAMPAIGN ID: 04V182000
RECALL DATE: 2004-04-20
SUMMARY
ON CERTAIN PASSENGER VEHICLES, UNDER CERTAIN ENVIRONMENTAL CONDITIONS, A VAPOR LOCK IN THE FUEL PUMP COULD OCCUR CAUSING THE ENGINE TO STALL. IF THIS WERE TO HAPPEN, THE ENGINE WOULD NOT BE ABLE TO BE RESTARTED FOR APPROXIMATELY 15 TO 20 MINUTES.
CONSEQUENCES
IF STALLING WERE TO OCCUR, THE DRIVER WOULD BE UNABLE TO MAINTAIN VEHICLE SPEED OR ACCELERATE, INCREASING THE RISK OF A CRASH.
REMEDY
DEALERS WILL INSTALL A RESISTOR IN THE ELECTRICAL LINE POWERING THE FUEL PUMP IN ORDER TO PREVENT AN OCCURRENCE OF VAPOR LOCK. THE RECALL BEGAN MAY 11, 2004. OWNERS SHOULD CONTACT BMW AT 1-800-831-1117.
COMPONENT AFFECTED
FUEL SYSTEM, GASOLINE:DELIVERY:FUEL PUMP
Vapor lock? Would explain the first incident back in early July when it wouldn’t start after I drove it hard, then was able to start after resting overnight, and the second incident today when it wouldn’t start after sitting in the driveway for a couple of sunny days.
