Fiat

I found a pipe that had come off the carb on my punto, i traced it back and connects to some sort of air regulator, i reconnected it, since my engines idling speed is up and down and then just constantly revs, i have replaced the sensor but nothing happened it does the same, could someone tell me what the problem could be, i have been told it could be the oxygen sensor in the exhaust or the temprature sensor how do i test these without replacing them.? help my car is due its mot at the end of the week and will not pass as it is, help !!

Vacuum leak, may have to reset computer