1997 Holden Commodore Major Service

Hi I have changed my spark plugs today and leads
The car is Duel fuel I have purchased new spark plugs but I did not notice that my old plugs where flat on top and the ones I purchased had a hole on the top the car started back firing so I put the old ones back on, But the car was still not idleling correctley and I had to put my old leads back on but my old leads are broken on 3 cylinders the little wire on the inside of the lead that connects on to the sparkplug comes out the car is still not running corretley it goes ok on fuel untill I push the car a little bit it starts to shakeand it does not want to go on gas at all, The new spark plugs are BOSCH YTTRIUM and the LEADS are MAX 300TOP GUN HEAVY DUTY LEADS not sure of what to get I have gone to AUTOBARN to get this staff they gave me the advise to get this service needs, also there is a small pipe connection under the throdle body and there was a loose pipe that air is coming out from the pipe is connected to the back of the motor near the drivers side I connecterd the pipe back on went for a drive a I herd this bang and the pipe blew of not sure what this pipe is for under the thordle body and if it has to be connected,
Can you please tell me what I am doing wrong

Thanks.
Tony H.