97 should be total drive by wire, ( the inline 6 was by then ) The pedal position sensor is on the left fender. This is a dual pot system where the computer compares both to confirm one has not failed so I'd expect a code to be tripped.

I'd pull the trans computer and look for oil. When the trans connector bushing fails, oil wicks up the wires. Oil on the circuit board isn't the problem, it is the graphite from clutches mixed with the oil that cause issues. Cleaning the board should work although I've seen an oiled board with no ill affects. If you swap trans computers, get one from another 420 because the smaller engined cars had different trans ratios and you will go into limp mode. You will also need to match rear end ratio also.

Does the ASR triangle blink on hard acceleration? Do you have an ASR off switch? My 97 SL320 engages ASR too early and will pull the engine down. I'd try driving with the ASR off. Well, the switch actually mutes ASR rather than a full torn off, you would need to jumper a pin on the 38 pin under hood connector.