Q: low gas mileage, bad exhaust smell

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Engine idles quietly, but has 'hiccups' or what feels like very small misfires, not enough to turn vehicle off or to change the RPM gauge, but I can feel it. Exhaust smell is not normal and smells bad. Very low gas mileage, normal 21-22 mpg, now only 14 mpg. The vehicle does have a little exhaust leak. All of the above have been symptoms of the last 6 months (I don't drive the car every day, maybe once or twice a week). Engine light came on yesterday with the codes P0170, P0171. Replaced the spark plugs, rotary, rotary cap, and air filter last month in the hopes it would correct the symptoms, but to no avail.

My car has 258000 miles.
My car has an automatic transmission.

Dependin where the exhaust leak is can cause the O2 sensors to not get correct amount of gases in the exhaust and cause the rich running condition. I would suggest having the computer codes pinpoint tests be done to see if the O2 sensors are bad or the exhaust leak is causing the problem if it is above or near the O2 sensors.

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