BMW Repair: cold start valve, fuel pressure regulator, fuel pump relay

Question
hi ron- i have a 1984 318i.i renewed the fuel pump, fuel pressure regulator, drained the gas tank and filled with fresh gas. this i find out that i still have the same problem.  it will not start unless i use the gas pedal and will die if i let off of it.  there is no voltage at the cold start and there is no voltage at the thermo start switch.  there is a black and yellow wire you are supposed to check for voltage on the thermal switch. it goes over to the fuel pump relay and when i apply 12 volts to that wire, the car tries to start.  can you explain why there is no voltage to the thermal switch?  thankyou and God bless you, jon  

Answer
The cold start system works only while the starter is ingaged and then only for a short period of time depending on engine temp.
It doesnt do anything unless the starter is operating.If you car will start but not idle you need to check elsewhere.
I would check the airboot for cracks, the MAF senser, a weak coil, etc..