I recently brought in my 2000 Frontier V6 for service at my dealer. It was shaking and shimmying on idle and the "Service Engine Soon" light came on. I asked the service advisor to check the light and the shimmying and also check why I get lousy gas mileage. I assumed all the issues (shimmying and gas mileage) were all related but my dealer said it was 2 separate things they found when they hooked up to diagnostics. The shimmying was due to misfire so they recommended injector flush, lousy fuel mileage was due to "Knock Sensor" fault. I had them do the injector flush which fixed the shimmying very nicely. But replacing the Knock Sensor for the gas mileage problem was extremely expensive so I held up on it. My question is, "does a faulty Knock Sensor lead to poor gas mileage? and will replacing it fix the problem?" Or perhaps is this a tune up issue? You thoughts on the issue will be greatly appreciated.