My truck has 250,000km and surging and bouncing rpms when it's given a shot of gas. Makes the truck hard to use when I'm off roading because it will jump around. When I scanned it I got a code for the Mass airflow sensor.

When I checked it on live data it was pulling 4.5 gm/s at idle and 18.5 gm/s at 2500 RPM. I went over the engine with propane to see if I could find a vacuum leak. Next I soaked the entire engine in water to see if I could make it stall and it was good.

After that I checked the rest of the live data values and found long trim fuel trim bank 1 was at 17% and bank 2 was at 4.5 %. I checked the fuel pressure at the rail and had 60psi. I performed a leak down test and it dropped 9 psi in 10 minutes. Could this be a leaking fuel spider or pressure regulator? Truck starts on the first turn everytime and has okay power. Has been bad on fuel mileage but I also have it on 31s, roof rack and loaded with off roading gear.

 

Leakdown is meh, do a dead head pressure test at the fuel filter following the sticky. that will tell you if the problem is in the tank or the upper intake, your '05 has the MPFI Spider injection assembly so it could be either a regulator going out, cracked injector hose, or a cracked metering block/failed seals. the latter 3 options being extremely rare/never seen. the other much more common problem is a failing pump.