Tune-Up Question

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The things that matter most are the air filter, front oxygen sensor, and the mass airflow meter. If the oxygen sensor has over 50,000 miles, change it. Also, an incorrect reading from a coolant temp sensor can cause a rich mixture. These things can all be observed and compared to benchmark readings on a labscope.
Bill Ditmire Ditmire Motorworks,Inc. 425 White Horse Pike Absecon,NJ 08201 http://www.ditmire.com 609-641-3392
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.