aristo gs430 missfire on kickdown

[turbotezza]

hi guys im in need of a little guideance please ive recently brought myself a toyota aristo v300 2jz gte badged up as gs430 its a lovely machine but i have a problem with it i need to resolve ,it starts perfect and runs perfect revs up fine, drives fine, pulls great until you kick it down it seems to missfire , will change sparkplugs to rule them out ,which are best budget ones??..also its doing really bad mpg i know its never going to be good but i think its doing about 10mpg! 

thanks for taking time to read ,,,steve

[TigerFish]

I would expect better fuel consumption than that, unless you are ragging it around, in which case you will see values that low.

 

Are there any stored fault codes? Does it do the same if you manually select gears and accelerate as hard as you can without kicking down?