Throttle Position Sensor

I've been having trouble getting my TPS fixed. There were three codes that popped up saying:
P0171 System was too lean (Bank 1)
P0172 System was too rich (Bank 1) and
P0120 Throttle; Pedal Position Sensor; Switch A Circuit
The mechanic I brought it to did some basic maintenance and it took the check engine light off for a day or too, but my truck still starts to idle and die if I don't give it any gas. Please Help.