Hi all, some help would be appreciated

I have a Fiat and recently the exhaust pipe broke from the middle
(near the filter of silencer) I left it running without changing it
and then I went abroad for 2 weeks and I left it parked and
disconnected the battery (I think causing the ECU to reset) then after
3 days or so, the Engine is running half the speed, jurking and
missing (it?s working only on two spark plugs)

Could there be a sensor in the silencer that caused the ECU to
function at half the power or it?s more likely that the ECU is damaged
?

If it?s a sensor, Could I disable it and reset the ECU and see if it
works?

Pls help

Thanks