no
With it
for any car to get better gas mileage get a better flowing intake and/or exhaust or get it tuned
Clean oil lubricates better, it is "slicker". If the engine can spin easier, that will improve fuel economy.
depending on your driving, it could increase up to 4 or 5 mpg. But gas mileage will be determined by driving style.
No
No, I don't think they would negatively effect your gas milage. You just need to make sure that you keep them with plenty of air. That is what would negatively effect your gas mileage.
I am not 100% sure, but I'm quite certain that adding an aftermarket performance exhaust, (one that is designed to increase horsepower through decreased backpressure) will in fact increase your gas mileage. This is as long as the nice new sound doesnt give you a lead foot. Basically, if you retain the same driving habits, a performance exhaust should improve you gas mileage.
YesYes
If it is malfunctioning it can affect fuel mileage.
yes
In theory, removing the exhaust pipes or cutting holes in them could increase the gas mileage. However, in most states it is illegal and could cause damage to the valves inside the engine.