I've been down this road also.  I would recommend you buy a pressure
gauge and check the fuel pressure.  If your fuel pump is more than
three years old it may be giving out.  Pressure should be 25 to 35
psi.  A new fuel pump will put out almost 100 psi.  Check by pinching
off return fuel line also.  The one coming out of the dampener.  You
need an oscilloscope to check the sensors.  They produce about two
volts.  Cannot be checked with multimeter....too much impedence.
Sensors can come loose.  Need to be about 0.8 mm from mark and ring
gear.  Depends on year or manuf.    Check the fuel pressure first.

======================================================================
* Reply by Jack D. Russell, Sr. <jackru$$ell2@notmail.com>
* Newsgroup: alt.autos.porsche.944
* Reply to: All;  "GTi_roadkill" <gti_roadkill@yahoo.com>
* Date: Fri, 08 Oct 2004 22:04:47 -0400
* Subj: 86 944 Trouble running after short warm up
======================================================================

Gr> Have read most of the posts already similar to this.
Gr> Initial problem started while driving on the highway after 10 mile
Gr> shopping trip.  Car would run fine unless it was revved above 3-4K.
Gr> Once it was revved up, it would die. After waiting a couple of hours
Gr> (time enuf to get tow rope), it started and ran fine back home as
Gr> long as it was babied.  Now it starts OK, then dies after 20-30
Gr> seconds when the DME relay is bypassed.  Fuel pump runs fine,
Gr> voltage is OK to the coil and fuel injectors with the DME relay in.
Gr> Already replaced fuel pump and fuel filter, have tried new DME relay
Gr> How long will the car run if speed or reference sensor is bad? How
Gr> about the fuel pressure rgulator?
Gr> The car only has 43K miles and the story is that it sat for 5 years.

Unplug one injector and see if it will stay running more than the 20-30
seconds you mentioned. If it does, you have a bad FPR. Check all of your
vacuum lines for cracks or leaks. 5 years of sitting does nothing to
help a car. Many problems can arise from it. Check that your filters
(air and fuel) aren't blocked. It's not unheard of to get a bad DME
relay new. Try a known good one. Good luck.

You guys are incredible!!  After changing the fuel pressure regulator, the
car starts and ran for 5 minutes without problem.  While I was at it, I
changed all the vacuum lines that were connected to the FPR.  So far so
good.

Thanks for the help.