I have a 1988 Toyota Pickup with a 22re engine. It have a problem that after about 2-3 minutes of running that if you don't have it to the floor it will spit and sputter and buck. I have changed Mass Air Flow Sensor, TPS, plugs, wires, cap, rotor, fuel filter, and check for any vaccum leaks. Code Reader gives me a code 51. Does anyone have a clue on what might be going on or what I should do next.

 

First, double check that the spark plug wires are on the correct plugs and double check the sensor and vacuum connections. Then troubleshoot the MFI system.

My FSM says that a 51 is the TPS idle circuit. Try readjusting the TPS and verify that you are getting the correct readings as per the FSM. Sounds like more than just the TPS adjustment going on, though. One or more of the sensors is sending erroneous information to the ECM causing improper fuel metering. You can download the FSM here http://www.ncttora.com/fsm/index.html Look for the '84-'89 4Runner FSM because it says it's specifically an '88. The engine will be the same for the pickup. In the EG (engine) section there is a troubleshooting guide for the MFI system. This is where I would start. You will be checking the output of all the sensors against a spec listed in the book using a Volt/Ohm meter. Start at the beginning of the Diagnosis System in the EG MFI section and go step by step. Somewhere in there is a sensor putting out bad info and you will eventually find it if you go step by step. Good luck,
Bugs

 

Check your air supply tube between the air filter/MAF box and the throttle body (especially the rubber flexi parts) for cracks or breaks.

 

51 is, as I recall, the TPS is not signalling IDL condition to the ECU when the jumper is inserted... i.e.: the throttle is not fully closed or the TPS is not adjusted properly to give the signal that the throttle is closed.
If the TPS does not signal IDL properly, the ECU will look at the O2 sensor for fuel mix feedback and can cause idle issues since the O2 does not respond fast enough for real-time idle mix. Also, timing cannot be set properly if the IDL signal isn't generated when the jumper is installed and if the TPS isn't adjusted properly to give the IDL signal, the ECU will also think the throttle is opened more than it really is. That will cause am overall rich mixture condition but that may go away once you're on the throttle and the O2 sensor can give reliable feedback to the ECU.

Nutshell- check the TPS and adjust as necessary.