fuel delivery issues (90 240sx with DE swap)

[SonGohanX]

I've been having this issue with my 240 for over a year now and I'm really at a loss to what it could be. The car will start and idle fine until put under load at which point it will jerk and sputter to varying degrees. Sometimes mildly, sometimes it will be almost undrivable for a few minutes.

After the car has been running about 5-10 minutes, the problem will disappear entirely and it will run great until its been left sitting for about 45 minutes or more. It also seems to happen less often if I let the car idle for several minutes before driving it.

I've replaced the fuel pump, (with a Walbro 190lph) the fuel filter, distributor cap and rotor, and coolant temp sensor. The injectors have been cleaned and tested and are working perfectly. The distributor was checked for wear and shaft play, and was fine. The ignition timing is set to factory.

Also, according to my plugs, I'm running very lean, and I really don't think I should be with a brand new Walbro fuel pump.

My current thoughts are to test a new fuel pressure regulator or possibly a new ECU.

Any insight on this issue would be very much appreciated, and I'll try to be informative as possible if you need to know any more details.

[snowyred180]

Check for vacuum leaks too. I had a broken plastic piece connected to a line that caused mine to idle erradically, and even stall. Some are connected to like the IAA valve, which controls the fuel injectors. Check for cracked hoses or lines too.

[SonGohanX]

I've checked all the hoses a while back. I couldn't find any that were loose, disconnected or damaged. I can check again though.

Would that cause the car only to act like this shortly after starting it?