Cutting out

[bighead02]

Hey all right I fitted a air intake months ago and had to take the t_piece off the rocker cover which connected to the air box and inlet manifold. My dad came round today and noticed this and advised me to plug the hole off the bit just after the inlet because was sucking in air and making the car idle alot quicker he also said that having done that, that it may take a day or so for ecu to adjust the ammount of petrol being put in but since doing this it has decided to keeping cutting out at junctikns or when chnging gear at low speeds just wondering that this would be considerd normal. I have spoken to my dad and he seems to think its werid and to keep an eye on it. It a 99 plate v reg 1.6 any help would be v handy cheers