Mercedes Benz repair: poor gas mileage, obd scanner, poor gas mileage

Question
Hi whunter,
     I have a 1989 300e benz with 142000 miles.  I checked last and it gets 13 mpg after last fillup. My mechanic told me to replace the o2 sensor and it may help.  Recently, had the fuel filter, plugs, wires cap and rotor replaced and same mpg.  The car sometimes hesitates upon initial accleration from standstill.  I had the tire inflation checked and was ok.  Can you help? I want to keep this car.
Thanks in advance.

Answer
Answer:
The most common issues are:
* Leaking fuel lines
* Dragging brake Caliper
* Bad alignment
* Bad wheel bearing
* Vacuum leaks from bad hoses, seals and/or gaskets
* Leaking injector or Seal
* Bad Air Temp. Sensor
* Cold Start Valve leaking
* Leaking E.H.A. Valve or Valve Seal
* Bad Oxygen Sensor
* Bad Water Temp. Sensor
* Failing Reference Sensor
* Wiring Harness damage
* Weak/bad Ignition Coil
* Fouled EGR system
* Bad/damaged catalytic converter can cause false O2 readings

Correct hands on diagnosis will save money.
Good MB Shops
http://www.mercedesshop.com/shopforum/forumdisplay.php?f=14

Automotive repair training book on line.
http://www.tpub.com/content/construction/14273/

Fuel Injection
http://www.mercedesshop.com/shopforum/showthread.php?t=142406

Mercedes-Benz Driveability
Evaluating Electronic Engine Controls
by Steve Brotherton, Import Specialist
Published in: ImportCar?‡, February 2001
http://www.mercedesshop.com/Wikka/EngineControls

code reader info
http://www.mercedesshop.com/shopforum/showthread.php?t=144773

Jim Forgione's DIY articles
http://pages.prodigy.net/jforgione/MB_S500.html

On-Board Diagnostics (OBD) scanner tools for MBZs... & VWs too!
http://www.mercedesshop.com/shopforum/showthread.php?t=167086