Throttle Positon Sensor Prob 2000 Nissan frontier King Cab XE (V6)

I took my 2000 Nissan Frontier to a shop and had a pair of oil cover gskets put on it. I got the truck back and it drove fine for about three days before the service light came on. I took the truck to an auto parts store and they told me that I was getting codes that indicated an EGR flow malfunction and a knock sensor circuit problem. I posted this problem on another Internet group and a guy who is suppossed to be a Nissan tech told me that it sounded like the throttle body sensor to him. I know that the sensor had to be disconnected in order to put the valve cover gaskets on. When I got the truck back, I looked under the hood and wondered if he had crossed the connectors on the sensor, meaning, if he had his positives and negatives missed up. Is this possible? How can I tell if the TPS is not plugged in properly. I have had this truck since it was new and the service engine light has never come on. I have 180K miles on it and need it to last as long as possible. can some one help?! I am taking the truck back to this shop Tuesday anyway if I can't resolve the problem.