Check engine light came on & engine running at very high RPM 1992 ES300

AAA came to jump me, thought I had bad battery even though it's only 3 months old. Ended up being loose
cable. They checked charge, starter, altenator, etc.

When I got ready to leave car was running/reving very high, like accelorator semi-stuck.. I checked, fine started
to drive stepping on hard at stop to see if it would idle slower.  Sort of, but then back to high, car would drive
itself after stoplight when foot taken off brake. Slow, about 30 mph.

5 min later engine light came on, I drove home another 5 mins. In garage for 48hrs. Just tried to start to see if
light still on & it is, also reving high again, won't go down when stepping on accelorator to make slower.