harrier warranty and DIY..+car runnin wierd

[blackers10]

Hey guys
I have another question(had alot recently LOL)

I have the harrier warranty that ford gives ya free with purchase of a 2nd hand car..

the thing is.. im a firm believer in DIY servicing.. and obviously its MUCH MUCH cheaper..
i am wondering what i can do DIY that wont screw with my warranty..

i need to change my brake pads soon as they are running low(ford rekons 8000k left on em when i had my service on thursday)
i dont wanna pay them $180 odd to do 2x front pads.. when i can do all 4 for less..

now 2nd question my 99 au fairlane has been running wierd under acceleration.. and its worse when the out side temp is cold(late at night in winter for instance as it is currently.. car is upto temp tho)..
it feels as tho the engine sorta cuts out.. like a severe missfire..
but it ONLY does it under hard acceleration from 0-60(off traffic lights usually)..
the more i accelerate the worse it feels..

do ya think its a missfire(dead sparkplug or lead) .. i am on a different tank of fuel to when it started doin it..
and it doesnt do it at idle.. or have a sign of a miss at idle or highway cruisin speed or when im sittin on a constant speed..
any ideas please give them

thanks fellas