Idles rough then surges

My mechanic is having a hard time trying to pinpoint my cars problems. It idles and runs really rough and if I step on the gas the car surges.The plugs and wires are new, I had those replaced to see if that would help. The computer shows numerous false errors like that it is -40 degrees or that the mixture is to lean or too rich. He has swapped ot the computer twice and checked the sensors but they all check out good. What could be causing this problem?
:banghead::banghead: :banghead:

Stop swapping out PCM's and change the coolant temp sensor. If its telling the computer that its negative 40 outside, for sure it will run rough. Besides its like a 12 dollar part, and its very easy to do.