Blazer cold start

i have a 1995 chevy blazer midsize 4.3 liter engine with approx. 160k miles. last month it developed a problem where it would not start when cold(overnight). engine will start when ether is sprayed into the intake and continue to run on it’s own once started. it starts ok when the engine is warm (above 100F water temp). fuel pressure was checked and is within spec. i have replaced plugs/wires/rotor/cap/air filter/fuel filter.the fuel pressure regulator was also changed on a whim. fuel tank was drained and refilled with new gas. have checked all the sensors capable of being checked with an ohm-volt meter. vacuum lines were also checked for breaks/leaks. pvc valve is ok. ambient temperature does not seem to affect the fault that i can tell(parked in garage/full sun). there are no blown/suspect fuses. all power connections are clean/ battery is fully charged.

any ideas?.