Rough idle Mazda 3
Rough idle, bad gas mileage on Mazda 3 with the 2.0-litre engine
A vacuum leak can cause both a rough idle and poor gas mileage. And on this vehicle the positive crankcase ventilation (PCV) valve hose can leak and be very hard to diagnose. Even professional shops with smoke machines have a hard time finding this one. The hose is located under the intake manifold. Since new hose is cheap, try replacing it and the PCV valve and see if the condition improves. I’m betting it will.
© 2012 Rick Muscoplat