Adding a BOV to your 7mgte will not affect your idle in any way...
Venting to atmosphere will cuase you to run rich when shifting. This can cuase stalling and other issues, people have added a BOV with varying results.
Do it right, Do it once..
Buy nothing from ebay...
Stock BOV functions fine with stock turbo and fuel system...
Think about your upgrade order and do not piss on your limited(assuming since your on ebay) funds.
http://www.toyota-supra.info/forums/...mk3-supra.html
Good places for parts
www.horsepowerfreaks.com
www.titanmotorsports.com
www.driftmotion.com
www.arizonaperformance.com
www.beechperformance.com
www.bicperformance.com
www.rockauto.com
www.shop.retro-spec.net
www.mvpmotorsports.com
www.toyotaworld.com
http://www.jscspeed.com/
There are plenty of places that support the supra community and dont make cheap chinese low quality parts...