Austarion

Lately my stock JB has been revving at 1600 to 2000 revs at idle.
To fault find I disconnected the TPS & it went back to normal idle speed.
Then it started fine & am still driving at present with it disconnected, which surprised me.
It is a little doughy just off idle & I think my fuel economy might be worse.
No detectable pinging and otherwise seems okay.
Are there other downsides??

TPS is used to tune for transient conditions mainly. You'll find if it's idling, and you floor the throttle, it'll almost die, then pick up? That's because it's not giving you any 'tip in' enrichment (what an acellerator pump does on a carb).

Your enconomy will definatle be worse too, as the ecu will never cut the fuel on decelleration, the flip side of the issue above.

Should be able to get a TPS pretty easily? Testing your old one is pretty easy too to see if it is actually stuffed. Definatley replace it, as they're one of a majour sensors the ECU uses to corretly fuel the engine. There are a bunch of late 80's mitsies that use the same TPS, but with a different plug on the end I'm pretty sure, swap the plugs over and you should be good to go.

Second that. Check the TPS, perhaps it just needs setting to the correct position to fix your high idle issue?

Swapped in a replacement TPS & associated loom & trim pot. Perfect!
The old one seems to have no proper internal motion...tis stuffed.