WHAT ARE THE SPECS FOR FUEL PRESSURE, HOW MANY P.S.I SHOULD I HAVE IN FUEL LINE? 89 NISSAN P/U 2.4L

Has your fuel filter been replaced at all recently? If it hasn't, you could have a clogged filter. Sounds like a fuel delivery problem but it can also be caused by other issues such as ignition problems (spark plugs, wires, etc), fuel injectors, timing.

The first thing I'd do is relieve the fuel pressure and test the fuel pressure. You'll have to "t" in an adapter into the fuel line in order to check it. It should read between 38-44 PSI but double check to make sure that's the correct spec for your vehicle.

See if the fuel pressure drops to below specs when the engine is revved. If the fuel pressure isn't within specs at idle or when revving the engine, I'd suspect the pump needs to be looked at further as the culprit of your problem.

If the fuel pressure checks out, the next thing I'd suspect is a vacuum leak. But vacuum leaks will usually smooth out at higher RPMs, and you won't notice much of an issue driving until you're driving at slower speeds, or at idle. A bottle of water and soap spraying around the possible leaking areas (intake manifold for starters) is a good way to find them.

Sounds like a low fuel pressure issue or a stuck open egr valve/air leak.

Change the fuel filter, there is also a gauze filter in the fuel line banjo at the injector pump.

engine could have faulty clutch fan causing engine overheat or fuel pump going bad,soon as car stall out check fuel pressure with engine off.if you have 80 to 90 psi with new fuel filter fuel pump okay.if you have zero fuel pressure fuel pump not pumping any fuel.

you got air in the fuel line,you need to bleed the fuel line then it will run fine.

You have a leaky fuel pressure regulator or injectors. Youre fuel filter may be clogged as well

the gas cap can make your check engine light come on do to not enough vaccum in the take for your evap system and it could cause the vehicle to run a little funny. but highly unlikly this is your problem.if there are no trouble codes or no check engine light this could be very hard to diagnose on-line you may want to take it to a respectable mechanic and have them run an on board diagnostic test on it

Check the vacum line to your fuel pressure regulator, the line may have a crack in it or the regulator may be bad. 

If you engine is a 2.4 liter it's on the passenger side center of the engine compartment, the hoses from the fuel filter conncts to the throttle assembly . You may have to remove the air filter housing to see it. It is a round canister hoses held on with fuel line clamps. hope this helps

engine oil breathers blocked remove and flush out.hope this helps please let us know.adrian