Hard start after 3 week sit.

[fixkick]

oops your read , about 1/2 throttle starts. (yes)
sure, this is the case only on engine with a bad IAC, valve.
the engine has dead thermal IAC and there is no cold starting air now, and to start the car it floods , and sure 1/2 throttle or even 1/4 adds this missing air and avoids the flood, just one of many types of failure.
The ECU does not know the iAC is dead so inject fuel based on the lie, with full IAC AIR but there is no air so it must flood and stall.

so that is what you read Im sure.
if it only starts with 1/4" throttle even 1/8" the IAC may be dead. (cold start fresh air valve)

wish i knew what engine is there.
my 2004 had a v6 .