My '91 Previa has shown an intermittent Check Engine light for the past year. Dealer couldn't find anything wrong; but the engine labors at idle, lacks a bit of power, and occasionally stalls, esp. when sitting nose uphill. I just managed to catch the OBD1 trouble code 2-1. What does this code indicate? I'd like to have the answer in hand when I return to the dealer, so they don't hose me another $100 to say nothing is wrong. Many thanks!

PS: It has a new fuel filter, platinum plugs, and premium wires.