I've got a 944 turbo with a problem I think I just solved
(see my post '86 944T - Runs at idle speed only when cold?),
but I had to research some similarities with the 944.  Your
problem might be related, and here's something you might
want to check - it's an easy test.  

The Throttle Switch in the 944 NA (and 944T) tells the DME
when the driver lifts his foot off the accelerator.  If the
RPMs are high and throttle is closed (trailing throttle
condition) , the DME shuts off fuel to save gas.  My switch
was bad.  If the switch fails open it tells the DME the
throttle is open, and it will run fine, but use more gas.
However, if it fails closed, or if bits of the switch were
to rattle around and occasionally short the connections as
you were at speed (RPM>1600) it would suddenly shut off gas.

Perhaps it's a long shot for you that your switch is
intermittently shorting out, but when I tested mine, it was
very flaky, occasionally shorting when I snapped the
throttle closed, occasionally staying open, occasionally
staying closed even when the throttle opened.

You may need to check for your model, but on mine, the
throttle idle sensor switch went to pin 2 of the DME plug
(take off plug, measure with ohmmeter to ground should be
less than 10 for throttle closed, open for throttle open).  

You can also access it for testing at the switch itself -
for my 944 T it's on pins 4 and 6 of the switch.  The turbo
also has a throttle position sensor (potentiometer) that is
integrated into the switch (pins 1-3) that is not found in
the NA.

You should be able to just disable the switch and drive it
around for testing,  if your problem is intermittent.
Search in the "944 shudder" for more info.

Firstly, very many thanks to all who offered suggestions as to why my late
'85 944 Lux was spluttering & losing all power intermittently ( see my post
1 August ).

Since then, I've replaced the DME relay, the ignition coil, the fuel pump
and the fuel pressure regulator, all to no avail. It's had a new plugs,
dizzy cap & rotor arm recently too. The problem first arose when I was
driving at about 60mph - there was a muffled thump noise and the car died
totally just for a second, then picked up again. It keeps doing this, but
there is no pattern apart from it seems to do it a lot more going uphill.

Please - has anyone got any more ideas, as I am tearing my hair out now in
frustration !!!!!

Cheers folks.

Myles