Dirty fuel?

Start with the simple things like fuel filter.

I run a dual fuel filter system in the Prado.
I run through a CAV filter first then into the Toyota one.
The CAV filter has a clear glass bottom so you can see if you have a problem and I carry a spare just incase.
They only cost about $7.00 for the filter after the initial set up of aprox $100.00

Andy.
The symptoms you describe are not consistent with bad fuel, the most likely thing is a crack in the plastic insulator around a spark plug, if you pull out the leads one at a time and look very closely at the sides of the insulator you will find a black mark where the spark is breaking through. Eric.

a note on dirty fuel.............
If when you pull up at a servo and there truck is there filling the tanks, drive on to the next one, it stirs up all the dirt and water ect in the bottom and you get a tank full of cruds....

andyq

Dirty fuel can be picked up anywhere.
One thing you can do with petrol engines, or should I say, used to be able to do to them, is to put in 2 or 3 lts of Metho. Apparently it can soak up to 3-4 times its own weight of water contaminates

I also like the fact that someone has said to run your vehicle almost out of fuel before you top it up again , and change the filters.

If you are slightly mechanical, or have a couple of mates that are, another thing you may well consider is dropping oout the fuel tank, and give it a good clean out.
Put it all back together, with new filters.

An inspection point is to remove the sender unit/inspection port from the tank, and have a look inside ( with a torch, and a mirror ) to see if the tank has crud on the bottom.

Hope this helps
Cheers
Bucky