Starts for an instant then dies, over and over each day. Also if sits for a while have to go through the whole hard start all over again. Weather is warm and nice, no cold issues. MAFS was replaced recently as that was defective, but still having lots of trouble with starting and low idle. Cold start hardware? Ideas?

-shoe

It reads like cold start injector system is working for approx 8 seconds, then dies. Of course, you hear the tank fuel pump work for 2-3 seconds, otherwise, it would not start.

At ALDL connector, short pins A to B and turn key to ign, no start. This places ECM into diagnostic mode and extends IAC and opens all ECM solenoids, EGR & Purge. Unplug IAC.

Turn off ign, unplug short, turn ign on for 15 seconds allowing ECM to close all solenoids. Turn off ign, then start engine, use gas pedal to keep engine running to operating temp. Once operating temp is reached, set base idle for 650-700 rpm, you may have to pull plug to use Torx screwdriver, T15 or T20, to adjust throttle blades.

Once base rpm is set, turn off engine and plug in IAC and disconnect battery for 15-20 seconds to erase trouble code. Turn key to ign ON for 15 seconds, this allows ECM to count out idle setting of IAC.

Start engine and idle should be ECM controlled, meaning selection opf A/C or DEF, turn on headlamps, or turn wheels, or select a gear, idle will remain the same. IAC should be warm to the touch. If not, then use DMM and monitor pins a to b and C to D. These are the ECM commands to open/close IAC to control rpm. No action, bad ECM driver or faulty wiring between the two items. Make sure with ohmmeter, these pairs of wires are not shorted to ground.

Another place to check is engine ECM coolant sensor and its harness. Sensor should read 10K and above at 70°F, er, above 5K. Two hundred ohms at operating temp. Same with harness here, no shorts to ground and you can read continuity of the ECM circuit from the connector.

Remove vacuum hose at fuel regulator to ensure no fuel inside hose. If there is, replace regulator.

Good luck.