Hmm... '91 is pre-OBDII, so the engine management system isn't regulated by any standard. Hence we don't know for sure what is and what isn't monitored or controlled by any ECU that might exist.

But whatever, 7-800 rpm is a typical hot idle speed, 1500+ is definately wrong. Question, does it idle irratically? If it does, then an airhose leak might be to blame. Most cars have crankcase breather hoses that feed crankcase fumes back into the engine so they get burned rather than emitted as pollution, and a leak here could be an issue.
The other distinct possibility is that the choke is never going off - you'd know this because although the idle is high, it is fairly consistent, and the car probably smells a bit of gas. Now if your car is ECU controlled, then I'd expect that this could be an ECU fault, or a temperature gauge fault. (Does your temperature gauge work??)
Oh, and check your radiator fluid level too. (When cold obviously, unless you enjoy getting scalded). If the fluid is too low then it may not be circulating properly, resulting in a hotter than normal engine - which would cause a higher idle. (But in this case, it probably wouldn't be erratic, as the choke would also still be active for the same reason).