Help - Stalling after reving up

Hi Guys,

I have a problem that has taunted me for last year and a half and I have not yet found "the" solution to it. Here is what is wrong.

My car sometimes stalls when the rpm is dropped to idle from above 3000 rpm. That usually happens when I drive about 15 minutes. Even when the car is not on the run, if I rev it up and let it drop I can see the rpm drops down to below 500 which then the engine struggles to recovers itself (if it doesn't then it stalls). I also noticed that after having a drive for around 15 or so minutes, at idle, the engine rpm bounces up and down around 500 rpm.

I have Sti Year 2000 (version 6, the last type of flat head lights) with Blitz DD BOV. I have read from forums that it is dirty BOV that is causing the problem. So I have taken it apart, cleaned it (i mean I cleaned it really really good) which definitely helps but you can still see the rpm going below 500. Also the bouncing effect never stops.

Can anybody please help me how to fix this problem?
I would really appreciate it.

check to see when the rpm's drop if the BOV is closing...if it doesnt close all the way after revving, it will stall, u might have to make the spring rate in the BOV tighter