The 4runner has 200 Thousand miles on it, upon start up the engine begin to pitter out before turning off completely. The MAF has been replaced. so has the EFI relay. But the problem still persists.
Did you use the OEM part for MAF sensor?
Change the air filter, fuel filter and then pressure test the fuel pump.
Check for a severe vacuum leak
I would check and see if the fuel pump is working correctly. Do a pressure test but also remove the relay and jump it with a digital multi meter in the highest amps setting and insert the probes in the socket. Read the amps the pump is drawing. If it is a small number, then its weak. It should be around 3 to 5 amps or somewhere there abouts. If its very low or high then there is definitely an issue with it.
I had one of these and fuel pumps were a problem. They are easy to replace and you may want to consider putting a trap door in the floor to access the fuel pump since all is old and maybe rusty. Dropping the tank may not be a good idea. I had a trap door in my truck. Worked out great. I just put in a fuel pump from a ford and it worked well. These vehicles are not picky on the pump. They have a fuel pressure regulator that passes the extra. 25 pound Bosch system.
If the fuel pump is doing what it's supposed to do, I would possibly look into the ECU. My buddy has a 1995 4Runner that did the same thing... would start and run for a few seconds and shut down. Went over a ton of different things, turns out a trace on the ECU fell apart. Replaced it and now it runs fine again.
