This is gonna be long because I’m stumped and I dont know where to go from here. My brothers got an 03 Protege5 (MTX) with 187k miles on it. I assume the water pump failed and he drove it until it overheated to which it developed a loud knock and wouldn’t run correctly. (Apparently he doesn’t know going up to H means turn it off and let it cool, but whatever) Anyways, we called it dead and ordered a complete rebuild kit. Had the block checked and they okayed it, and we ordered a new head.

Heres a list of everything that we’ve replaced:
Cylinder head
Pistons + rings
crank + camshafts
timing belt + water/oil pumps
Crank pulley
cam + crank sensors
ignition coils/wires/plugs
fuel injectors/regulator/dampener
all three of those vaccum solenoids up top
MAF
IAC
Clutch(also rebuilt the transmission while we had it out)
TPS

Things not replaced:
fuel pump
PCV valve
not sure what the sensor that just sits on top of the intake hose is
also not sure what the sensor beside the MAF is

The issue is, it used to crank and start fine, but now it will crank strong (and is perfectly in time) but won’t start cold unless I hold the gas to the floor, and then it will die. And I’ll keep trying to crank it. Eventually I can crank it without pushing the gas. And it will rev up high to 2k then slowly drop. When it gets to 1k it stutters and dies. UNTIL it warms up. Then it will crank and idle roughly at 600/700. I’m getting a p0300 and that’s the only code I’m getting. Like I said I’m stumped because I don’t know where to go from here.

Also, I can NOT hear a fuel pump prime. But when it does decide to run I can only hear the fuel pump when I have the cover in the back seat off. And then it’s kinda faint but I’m not familiar with how loud it’s supposed to be on this car. If you need any other info please let me know and I’ll tell you what I can.