Where is and how do I remove the cabain Air filter in the V6 2003 Eclipse

 

your 2003 doesnt have one, unless installed by you (or a previous owner).
eclipses came with one from the factory until 2000... after that it was deleted and requires installation.
if you wish to install one, you need to remove the glove box and glove box liner. Then you need to cut out the plastic "blank" that currently resides where the filter would go.

 

Thanks for the quick update, I'll return the filter that parts store happily sold me.
I hunted everywhere for its mounting, even the "Car users guide" mentions that it needs to be replaced.

Biggles

 

like I said, it MAY need replacing if it has been installed by someone. Unless, of course, you've owned the car since new, in which case it obviously wouldnt have one.