Do I need a timing light to adjust idle speed?

I replaced the original oxygen sensor (Toyota part # 89465-19265) on my 1985 4-Runner,22R-E,W56 with an NGK exact fit (NGK part # 24105) and since then after the engine has reached operating temperature and closed loop mode (thermostat opens) the idle speed begins to drop from

750 RPM down to 550 RPM (I think). Do I need a timing light to adjust the idle speed screw located on the front of the throttle body after the engine has reached closed loop?if not do I still need to short the check engine/timing connector to perform the adjustment?. By the way I don't have a timing light if I need one,so is there someone in Dartmouth/Halifax,Nova Scotia that has one that can adjust my timing?.Thanks.