In these days of electronic ignition and fuel injection, there's little to do in a tune-up besides changing the spark plugs and maybe the spark plug wires. I would just explain to the mechanic that fuel economy is low and ask him to see if any diagnostic check pinpoints a cause. He might suggest plugging in a code reader, which depending on your state might be a regular part of the vehicle inspection emissions test anyway.
The oxygen sensor recommended maintenance replacement interval is 30,000 or 40,000 miles. It can go several times that and not show any obvious trouble, but if yours has never been replaced, you might try that. By upstream, I mean the one in the exhaust system before the catalytic converter. There's another one past the converter to monitor its performance. A failing O2 sensor is said to sometimes be a culprit in low fuel economy, since it monitors and fine-tunes the fuel-air mixture.
Thursday, July 3rd, 2008 AT 8:17 PM