I have what is probably a stupid question. My gas mileage has fallen to about 16mpg (96 E320) and the dealer said it could use a tune-up. It's just had it's spark plugs and oil changed, and since I'm assuming all timings etc are done by computer chip, what exactly is done to the car during a "tune-up" and will any of it help gas mileage.
Thanks
The sensors that the computer chip relies upon (O2 sensor, MAS, etc.) can age and cause declining gas mileage. Connecting a diagnostic test inistrument to the car will read the fault codes to determine if an emissions component has failed or is failing. You might also consider changing the air filter if it's been awhile, even if it does look fine.
To avoid replacement of recent plugs and oil, ask the dealer to pull the fault codes to see if an emissions component has failed. If it has, there's your answer.
You don't say what kind of driving produces only 16 mpg but cold weather driving really kills fuel economy. Don't rule it out as a factor.
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