My 1992 lexus sc 400 is jerking slightly and my engine light came on. I checked the code and it came up 13 for RPM fault circuit, so I took it to a local toyota dealer and they could not find the problem, with 3 hours diag time. I do not believe they checked the cam sensor or related, they just said that diag were done on ing,and related, and i recently replaced main ox sensor so this is new, I hope you have a good hunch at this point im lost.