well, starting to seem like something is seriously allowing leak-down of the fuel rails. Before the next cold start, maybe pull the plugs to see if one is wet with gas - could be a leaky injector?
ever smell fuel underhood?
hmmmm, doesn't seem to be fuel-related. you could try some starting fluid as an additional test
coupla not-great suggestions; inspect the large tube from the IACV - maybe it's cracked or partly loose. dunno why it would be worse when cold though.
clean the throttle body - check into the SeaFoam can with the nozzle. again, maybe gummy when cold....????
inspect spark plug boots for oil/moisture on those cold mornings? how old are the plug wires? is it dew-y on those cold start events?
Crank sensors have sometimes been known to fail at warm temps, maybe yours is flaky at low temps?
Of course - the difference in both quality and price between OEM and "the aftermarket" is a given. What I was saying is that massive price disparities exist among parts of equivalent OEM quality - that in the stated example, going to the dealer means paying three times as much for the same Mitsuboshi belt. That's all. Not recommending anyone "cheap out"; to the contrary, pointing out that the high-quality/low-price combination exists, so don't get taken.
Myself, I like Terry Pratchett's version of that old adage: Make a man a fire, and he'll be warm for a day. Set a man on fire and he'll be warm for the rest of his life.
yes, AISIN is commonly used by those wanting a one-stop shop for nearly subaru parts.
it's $260 +shipping with a 5% discount code at rockauto
while the coolant is empty and you have to remove the thermostat anyway, it's a good time to replace that with Subaru as well.
If possible - check first before buying parts. we're assuming unknown age/brand but is there any possibility some of it is new subaru once you get in there?
next time it has sat and you feel confident it would 'fail' , don't start directly; cycle from Off to On, wait for a 3-4-5 count, then back to Off, immediately back to On, count, Off - On. 3-4 times and THEN go from Off to Start. That should pressurize the rails if they have lost pressure.
Poor quality parts were used if this is failing 9,000 miles after replacement. Replace it all with Japanese parts.
If that's the quality of water pump used..... I would be questioning all of it including the head gaskets and the labor.
GD
Looked at his webpage 2 days ago & it appears he still is making adapters, just don't know if its Subaru EJ-Toyota W56 trans adapters.
https://www.billsautofab.com/
Contact him?