96 Land Rover Disco power and idle issues

Your electrical fault may need some more info to fix: exactly what is happening under which circumstances and what actions do you take the moment it happens. Idle is controlled by two main parts: the Idle Air Control Valve (IACV) and the Throttle Position Sensor (TPS). If the TPS is messed up, the ECU will go into limp mode and speed up the engine idle to keep it driveable to a place of repair. If the IACV doesn't close the idle air bypass on the throttle body, the engine will idle faster than normal due to lack of control of the air flow into the engine. Alternatively the throttle cable may be sticking, which is a lot easier to diagnose and fix.