Low economy could also be a sign of your catalytics being gunked up as well, I got mine replaced under warranty at 120,000km and it made a noticeable difference in power and fuel economy.
-Electric Frost
1998 Mercury Mystique GS
SVT side skirts, rear SVT bumper, SVT exhaust, K&N Cone Air intake, 17in ST200 rims
2005 Ford Mustang GT
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