93 240sx se coupe - Runs great cold, terrible after warmed up?!

[tkrolo01]

I mistakenly posted this under the KA section initially. I've got a 93 240sx se coupe with around 100k miles. Been messing with stumbling and backfiring for a couple of months and near my wits end. In its current state, it will start and run beautifully for 10-15 minutes, until it gets warmed up. After that, its like it isn't the same car. From a stop, you have to ride the clutch and give it extra fuel through 2nd gear or it will stumble and die. After you get going you have to continue to baby it by easing onto the gas or it stumbles and backfires, at times, violently. It seems to idle fine and run fine once you get to operating speed as long as you don't have to touch the gas. I've replaced the cap, rotor, fuel pump, filter, alternator, cts, tps, and adjusted the timing, but nothing helps. If you try to start it before it cools down completely, it takes several extended cranks to get it to fire. I've had advice to check the tps voltage, but it seems fine. I can't completely rule out the mafs, but based on all the work I've done, I think it has to be in the fuel delivery or ignition. I just bought a set of injectors hoping that this is my problem, but any other suggestions would be GREATLY appreciated. Thanks in advance.
Modified by tkrolo01 at 7:23 PM 2/15/2006

[le_ryan]

just a guess, but what about the fuel presure regulator.?

[tkrolo01]

I thought that also, but the fact that it operates normally after initial startup leads me to believe that it is alright. I just bought a rail with injectors and a regulator, so I may switch it out to see if it makes a difference.