2001 chevy S10 2.2l I4

after driving for short distances, ie down to the corner store or to the mailbox when i try to start the truck within minutes of shutting it off it will turn over but will not start unless i let it sit for a few minutes then it will fire right up and run fine.

with longer trips it will shut down and and restart just fine, leaving it over night it will start just fine.

this is not a recent thing, it happened early last year a few times and went away after happening 3 or 4 times without me doing anything.

if checked the fuel pump relays and fuel pump fuse, no issues,

the fuel pump and sender were replaced in 2018

the headgasket blew in october 2019 and the engine was pulled and rebuilt with most of the accessory parts reused

any idea whats causing this to happen?

I'm curious about fuel pressure when this is happening. I know you have a new pump, but still I'm curious about fuel pressure.

Also:

How many miles on it?

How many miles on the current spark plugs?

221k miles, on the odometer, engine has less than 2k on it since the rebuild.

plugs wires and coils were replaced when the engine was rebuilt

I havent tested the fuel pressure yet.

Wondering if his IAC isn't opening all the way. Orrrrr, his FPR is leaking fuel and flooding his engine.

Do you smell raw fuel after it starts during this condition?

Need to do some testing. I'm not sure the short trips is anything more than coincidence.

No gas smell on startup either when full cold or when its having the issue.

Cleaned the iac, still having the same problem.

Havent checked the fuel pressure yet.

If you can, next time it won't start, push down on the accelerator just a little bit to open the butterfly plate and attempt to start engine. If the engine fires right up, let go of the throttle, the engine may stumble a little, but should pick back up.

If you are able to do this every time you suspect will hard start, then your IAC is not functioning properly. Not that its gummed up, but its just a simple electromagnet.

Tested the fuel pressure this morning, 47psi static off the pump, fluttering 55 - 60 psi engine running and fluttering 38 - 41 under load.

Giving it a bit of throttle when starting up forced it to run so its most likely going to be the IAC thats failed not the regulator.

Got one on order, it will be here in a few days.

Pressure is low under load.