changed battery cleaned throttle body now engine light and fume smell

Mu battery died the other day so i got a new one. After it was replaced it was not idling properly. It was idling very low. My neighbor, who is a mechanic, said that the throttle body needed to be cleaned. He cleaned it. After that it was idling high so he told me to drive around and then the check engine light came on. It is reading a code saying system too rich bank 1. There was no issue with fume smells before the throttle body was cleaned. There is a heavy fume smell and it's ideling very rough and almost dying out. He thinks it needs a new mass air flow sensor. I don't want to spend a bunch of money on that if its not the problem. Any ideas? Thank you so much.