I've noticed that my in HG vacuum has changed a bit recently... When warm and idling it used to stay at around 15-16 hg depending on power load, but lately it's been hovering more at about 14-15. I recently installed an Apexi open air intake, could this be a cause? It's also pretty cold here, down around 30 degrees. My engine is at 59k miles. The engine may or may not be ported, I'm the 3rd owner, the 1st owner was the one who had the original mods done and only told the 2nd owner that it was "built to handle higher boost". Visible mods when I got the car were silicone hoses, boost gauge, dp mp cb. Most stock FD's pull about 17-18 hg, correct? Just wanna find out if my engine is about to blow or just running lower hg because of mods.

 

i had the same problem. as soon as i went to the greddy dual intake my vacuum reading went up to ~15. it was steady at 16 or 17. i asked this question and was told that everything was okay and that vacuum reading depends on alot of things. i know i didn't answer your question, so i too would like to know if this is happening w/ other fd's.
nick

 

It's normal for your vacuum readings to change when you change your intake..

I just switched from a pettit/K&N style intake with the accordian hoses, to an apexi power intake with hardpipes and larger filter elements. Vacuum went from around 16-ish to around 15-ish at the same idle speed..