OBD Code: System Too Lean

[hendrix]

4Runner: 2000 LTD 2WD
310,000 miles

New Parts:
All O2 sensors @ 308,000 miles (due to OBD code)
Fuel Pump @ 310,000 miles (just replacing parts at this point)
Oil Filter @ 310,000 miles (needed)
Air Filter @ 310,000 miles (needed)
New Shocks @ 305,000 miles (needed)
Bled brakes @ 305,000 miles (needed)
New Belts @ 305,000 miles (Routine Maintenance)(Power steering, Alternator, AC Belt)
Cleaned MAF sensor @ 309,000 miles*

Moderately New:
Timing Belt @ 215,000 miles (Routine Maintenance)
Water Pump @ 215,000 miles (Routine Maintenance)
New front & rear U Joints @ 215,000 miles (Needed)
Spark Plugs @ 145,000 miles (Routine Maintenance)
New Wires @ 145,000 miles (Routine Maintenance)

Problems/OBD Codes
The code it keeps giving is P0171 System Too Lean (bank 1), (too much oxygen in the exhaust.)
The first code that ever came up was cylinder misfires, 5, 2, 6 & 1 (8 months ago.) It would randomly come on and off, with different cylinder misfire each time. Then a code for bad O2 sensors (2 months ago), husband replaced them now the code for the System Too Lean.
The symptoms:
When I am driving in a steady speed on flat road it will loose power for split seconds (the rmp hand will drop to the closest lowest notch and then back up to where it was.) It will also do it several times when pulling a hill. The worse is randomly after I crank it up and start to drive. The first 500 yards or so it will only go 10-15 mph (sputtering) with the pedal on the floor, after about 500 yards it will clear out and run normal speed.

The other mystery is one day the Check Engine Light went off, I took it to get emissions and it passed, then with in hours the light was back on.

Any suggestions are greatly appreciated.

 

[drewm]

Best guess is that if it's multiple cylinders it's in the fuel delivery side, so you'll first want to replace your fuel filter, and then if you still have the issue, change your fuel pump.

Although from the sound of it, it's your fuel pump. Also check the fuse that your fuel pump is on, maybe it's loose or has a bad link.

Edit: I now read you already have already replaced the fuel pump. Check that fuse and change the fuel filter at this point.