Ok, check engine light gives me engine code 51. Here's what I found about that code.

SWITCH SIGNALS
IDL (tps) CONTACTS OFF, NEUTRAL START SWITCH OFF, A/C SWITCH "ON" SIGNAL TO ECU
WITH DIAGNOSTIC CHECK CONNECTOR SHORTED
--A/C SWITCH/CIRCUIT
--A/C AMPLIFIER
--TPS/CIRCUIT
--NEUTRAL START SWITCH/CIRCUIT
--ECU

Here's a little history. It's an 88 4runner, no A/C, recently swapped the motor. Now I am having a hesitation/surging feeling under a load. Along with lack of power and low gas mileage. It kind of feels like the engine could be starved for fuel. The timing is on, fuel pump works, so I'm thinking it could be a sensor or a vaccum line that's not connected right, and is throwing off the EFI. Any thoughts on this before I go on a sensor replacing binge. I'm thinking about taking it to a Toyota tech for diagnosis because If I just start replacing sensors it could get really expensive, and the ECU and EFI stuff is a little over my head. Any thoughts? Thanks

 

These engine codes are a bit obtuse. It looks to me like code 51 is telling you that your throttle position sensor is malfunctioning. That would be consistent with lack of power. I would check to see if the wiring is properly connected to the TPS. There are some threads on TPS on this site that should give you more insight into TPS troubleshooting.

 

check your fuel filter. i know its a pain but i was experiencing similar problems and found my ff to be like 80% clogged.

 

that is correct for that code but dont waste your money replacing stuff that may work fine go get a cheap multimeter they are $20 and check the sensors according to the service manual. also check the wires too cause they need to be in good shape or the sensor is irrelevant as the info never makes it back to the ecm.

 

I have the same code, I have already replaced my tps, and with old one, without one, and with new one, same symptoms, and same trouble code, 51, lemme know what you find, i will do the same

 

Well 14 years later and I’m having the same issue. New OEM TPS from 22re performance and it didn’t fix it. Did you ever find the root of your issue? The pigtail is brand new as well. I soldered it on last year. Idles like crap a couple minutes after start up and back fires through intake before dying when I give it as sudden surge of throttle.