The former Sheffield Wednesday and Cardiff striker netted in the 83rd minute to cancel out Heidar Helguson's first-half strike.
It was Rangers' first goal away from Loftus Road for more than 13 hours and came after the Pilgrims had failed to deal with a cross from Hoops captain Martin Rowlands.
Helguson went about things the hard way, however, missing the open goal at the first time of asking when his shot hit the post. The ball, though, rebounded kindly for him to slot home at the second attempt.
Rangers had a second 'goal', by Rowlands just before half-time, chalked off for offside against Helguson which was the first break Argyle had enjoyed all game.
They had seen defender Kris Timar's early shot ruled out when referee Kevin Friend decided the ball did not cross the line, and were denied a clear penalty when Kaspars Gorkss handled Jamie Mackie's cross.
Mackie went close at the end of the first half, but was denied by a superb save from Radek Cerny, and Argyle kept the pressure up after the interval.
Marcel Seip, Jim Paterson, Simon Walton. Luke Summerfield and Mackie, again, wasted opportunities as the home side chased the game by sending on wingers Craig Noone and Nicolas Marin.
It was fellow sub MacLean who finally undid Rangers when he latched on to Rory Fallon's headed flick-on, made space for himself and fired home a left-foot shot.
Rangers showed steely nerves to hold on for the point as Argyle tried to come from behind to win a game for the first time since Boxing Day 2007.
They survived plenty more pressure and a huge shout for a penalty when Hogan Ephraim handled Chris Clark's cross.