Most "non-starting" symptoms in Porsche 911 and 944 can be attributed to a defective DME Relay.
The Porsche DME relay contains 2 relays inside its housing.
The 1st relay provides power to the DME.
In the 944 Turbo, the primary relay powers the KLR ignition unit.
The 2nd relay provides power to the fuel pump.
This might be caused by broken solder joint inside the relay. This is why if you let the car sit for awhile, after the relay cools down, the car will restart.
One option that you have, if you do not want to buy another DME Relay, is to reflow ALL the solder points on the board of the relay.
This solution might cure an intermittent starting issue with your Porsche 993, 964, 944 and 911.
If you wish to buy a new DME relay 993 615 227 01 you can get the best selling one on Amazon Prime here.