Hey guys i recently did a jdm swap in my 98 (thanks to you guys and all the help). Truck runs great! No check engine lights or anything *knock on dashboard*. But when it is left sitting overnight or for a couple hours (4-6) I have to rev the engine when first starting or it will stall out. After 10-20 seconds of keeping the revs around 1500-2000 rpm i can take my foot off the gas and it will idle. The idle seems low though, 1100 rpm idle and sometimes drops down to 750-900 rpm idle. But after the truck is warmed up or hasnt been sitting long it starts perfectly fine and runs without any problems. My guess was fuel pump going bad? It did sit for over a year while doing the engine swap so it could very well be.

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Fresh gas is in the tank?

It will start cold without throttle? Or you must give it throttle to start also?

I have to give it throttle on a cold start or it will stall. Fresh gas in the tank. I have put close to 750 miles on it since the jdm motor swap and this starting issue has been present the whole time.

The jdm engines sit for awhile while transported and b4 someones buys them.

Id bet the idle control valve is stuck closed. Try changing the one from you old engine onto the jdm engine.

The one from my old motor is on the JDM motor. Everything is from the old engine except the long block.

It sounds like your motor has been sitting for awhile aswell. Are you sure yours is still good?
You can take it off and apply 12v to it and see if it operates.