ok. so i think i'll go for the spark plug wires. A quick question though, do i need 8mm or 10mm ones for better mileage? also would one or two disconnected spark plug wires lead me to get bad mileage? or it won't even start up at all?
If you replace the wires, get the 10mm, they will allow more current to flow. If you have one or more wires either loose or disconnected, it will significantly affect your mileage. How it runs and how much it affects you would depend on which wire or wires are loose, disconnected, crossed and so forth.
It will start and run, under some conditions. I have had two wires be crossed and the car idled ok, not great, but ok, but when I tried to drive it, it had really lousy power and took forever to get up to highway speed. It did run though, which surprised me.
I've had several cars run with crossed plug wires before. (It makes a great practical joke....)
Also remember to take into account for your tire size. Your new tires are 1.9% bigger than the old ones, so your MPG formula would look like this (odometer*1.019)/gal. Basically, just take your odometer reading for a tank of gas, multiply it by 101.9% to get the actual reading......then divide by gallons used. PM me if you want/need this in automagical spreadsheet form....