ok random question

i recently changed my exhaust with decat and it didnt have bits for the lambda so i just left them off,,,,, car ran fine ( well as it used to)

now i have just changed gearbox,,,, i had to disconect the battery for it and now when i start the car it runs for a few seconds,,,,,, the just dies and if i tickle the throttle it cuts out quicker

wondering if i need to reconect up the lamdas or not or could it be another issue i have ???

take into account that it did run before with the lambda sensors in the boot but i never disconnected the battery when i changed the exhaust hence me asking