I noticed this yesterday when I was behind a car that I could see the reflection. The left fog was flickering and then slowly went out. I turned them on and they work fine. Any ideas on what is going on here? Thanks for any help guys!

 

Sounds like a switch issue to me. Something is closing the circuit and causing power to run to the flickering fog.

 

Are you by chance running LED bulbs in your fog lamps

 

If they are xenon, the unit is starting to go bad.

 

They are the stock lights that came with the 05 so Im guessing that is the xenon lamps. Thanks for the info, I will start looking into getting a replacement.

 

You do know some W211s use the fog lamps as cornering lamps, I don't know how they work but you might want to check your owners manual.

And BTW the stock fog lamps are not Xenon.

 

The curb illumanation/whatever its called turns on the fogs with the turn signal or when you turn the steering wheel (via steering angle sensor).
I have a feeling previous owner must have put in LED's in OP's car.