2003 Pontiac Grand Am Check sensors

you can test tps with a dmm hook to signal wire then a good ground. then move throttle from closed to wide open throttle should be a steady increase from .7v up to 4.5v

o2 sensor can be checked with dmm to see if its producing voltage from .1 - .9 volts constantly changing

maf you can check for power and ground but not really how its reacting the meter is too slow.

best thign is use a scan tooll or a oscillioscope