I think 42 is for a speed sensor, speed sensor circuit, possibly TPS or AFM. IIRC, there are two speed sensors, one behind the speedometer, and one at the transmission. The one in the speedometer went bad in my '90, causing the ecu to think the truck was idling, even when cruising along at 75.
Code 51 is possibly TPS, A/C switch, A/C amplifier, neutral start. Where did you get the the new TPS from, was the original one bad?
If you have a Toyota dealer nearby, swing by the service department(if they are friendly) and ask to talk to a tech, they could likely give you an idea of what the code is most commonly linked to, rather than testing each one listed.
You can download a pdf file of the what the codes could be here
3vze Codes , main site here
Ebooksquad.com. The download is free.
