Hi, I have an 1988 Trans Am with a 350 crate motor with a LT4 Hot cam, and 1:6 rollers. 24lb injectors, SLP Runners, and headers, fuel pressure is set at 44lb, and I got a custom chip made for my mods.
Car was running and starting fine for the first two days. Then all of a sudden the car wouldn't start. The only way it starts is to press the gas pedal while cranking. And when it starts it runs too rich, and the rpm is at about 1000rpm. When you put the car in drive that rpm's drop to about 800rpm, but when you put it in park it revs up to 1500rpm and then back down to 1000rpm. No check engine light. I already changed the O2 sensor and the car still runs the same.
I checked for vacuum leaks and everything looks fine.

 

Does fuel pressure maintain after the ignition is shut off? How much pressure remains, and for how long?