Hello I have a Porsche 928 Model 1986 it starts once and if you turned off then try to started again it will not start until you wait a period of time to start again or you should remove the fuel pump fuse and crank then put the fuse back and the car start
plz help me in this problem
Regards

 

Easy stuff first - try replacing the fuel pump relay.

 

even easier,
smell the vacuum line to front damper.

NOTE if you smell fuel then its leaking and all the 3 parts should be replaced the two dampers and the fuel pressure regulator.
Instead of removing the fuel pump fuse,
hold the pedal to the floor then crank it till it starts.
How old is the
MAF,
CPS,
TPS short harness
O2 sensor,
fuel pump check valve.
Dampers and FPR