My boxster stalls...dirty filters again??

[Dave_Box]

Hi,
I was looking on some info on my boxster when I found this site.Exactly a year ago,my car will sometime stall when stoped at a light or stop.Problem was fixed by changing air and gaz filters.No probelm since until a few days ago.The car stalled 2 times within 15 minutes(restarts right away).Can it be the filters again??I fine it a bit too soon for faulty filters.There is no CE light on .When it stalls is like if I just turn my key off.Drove the car yesterday and today just fine,no stalling.I live far from any dealer and will appreciate any comments.Thanks.

I have a tiptronic 1999 boxster with 23000 miles
Mass air sensor was changes few month ago.