My '91 Z28 5.7 TPI wont start when its cooler outside!!! This morning it was 48 degrees and she wont start. I have been having this problem the past month, but the past week its been warmer when I try to leave for work. HWen I have been having this problem and it wont start, i can come back to it in a few hours when its warmer out and it fires right up.
In teh past 6 weeks, I have changed the fuel pump, filter, all injector upper and lower o rings, all fuel rail seals, the fuel regulator on the backside of the fuel rail, idle control valve, cap, rotor, plugs, wires, ignition module, TPS sendor,water pump, thermostat, coil wire,steering column with VATS bypassed.
I am completely confused now. On the flip side, when she is warmed up, I can be sitting at a light for about 30 seconds and she will stall out. The idle is set at about 700. I have to barely put pressure on the pedal to keep it running then, otherwise the the RPM's start to drop down and it stalls out. I am hoping BOTH issues are related to the same problem, so I can fix 1 thing. I cant imagine what else it is since i have replaced everything else that I can think of. Please offer ideas!!!!

 

Do a fuel pressure test & leak down test.
Do a resistence check on your engine coolant temp sensor. This sensor's resistence changes w/ temp. It is checked using an ohm meter or scanner, find the value on the net under "GM coolant temp sensor values". When the engine is cold it should be close to ambient temp outside.