I have a '97 GLE, auto. Couple of months ago CEL went on and I pulled codes 0304 and 0115. Was experiencing a little trouble cold starting and some rough idling. Mileage also seems off. So I went ahead and replaced the KS and reset the ECU. Next day, CEL was on and I pulled an 0505 code. Reset again, and a couple of days later (now) I got another CEL and have been consistently been pulling a 0115. What steps should I go through now? Replace front O2 sensor or Mass Flow sensor? Something else?

Thanks

 

0115
Diagnostic Trouble Code 0115 indicates a problem with the fuel management system on the right cylinder bank. The right bank is also called the rear bank. It is cylinders 1,3,5.

The Front Heated Oxygen Sensor for the right bank sent signals to the Engine Control Module indicating an excessively lean fuel mixture. The ECM attempted to correct this problem by directing the fuel injectors to supply more gasoline. Further signals from the Oxygen Sensor indicate that the attempt to correct the lean mixture condition was unsuccessful, and the fuel mixture continues to be too lean.

Possible causes include ...
- Intake air leaks
- Defective Front Heated Oxygen Sensor
- Fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow Sensor

 

wow, you dont get much more helpful than kevlos post...check that list, process of elimination im afraid...