my car surges at 70mph on 1992 Lexus SC300

it starts normaly, drives smooth, everything else operates correctly.

Asked by for the 1992 Lexus SC300
It could be many things, unfortunately and without experiencing the problem first hand or being able to do some basic diagnostic tests its hard to say. It could be a transmission problem, could be oxygen sensor related, a vacuum leak (but I don't think so at cruise intake manifold vacuum is low). Too hard to guess without being able to drive the car