Thread: vacuum pressure problem

Well I just recently got done putting the new motor in and now the car idles really rough. The map sensor jumps from 35-65 KPa. I noticed that my brakes also felt as though there was no brake booster connected to them. Anyways I found that when I caped the nipple on the supercharger that goes to the vacuum line to the brake booster, the car's idle smoothes out and map reading stabilizes around 45 Kpa. The vacuum line has no leak and the attachment lets air pass. I am thinking it has something to do with the brake booster ruining my vacuum pressure. Do I need a new one, or am I forgetting another vacuum line or something. If it needs to be replaced, is there a rebuild kit for it? BTW I was also expecting my supercharger to be loud enough for me to hear it. When I rev it I barley hear it or sometimes it is nonexistent. ON youtube there is some kid with a stock series 3 and he puts on K&N air filter and that thing whines so loud. I have full headers, HAI, 1.9 rockers and it sounds nothing like his. Why can't I hear her whine?

Originally Posted by comongoose

Well I just recently got done putting the new motor in and now the car idles really rough. The map sensor jumps from 35-65 KPa. I noticed that my brakes also felt as though there was no brake booster connected to them. Anyways I found that when I caped the nipple on the supercharger that goes to the vacuum line to the brake booster, the car's idle smoothes out and map reading stabilizes around 45 Kpa. The vacuum line has no leak and the attachment lets air pass. I am thinking it has something to do with the brake booster ruining my vacuum pressure. Do I need a new one, or am I forgetting another vacuum line or something. If it needs to be replaced, is there a rebuild kit for it? BTW I was also expecting my supercharger to be loud enough for me to hear it. When I rev it I barley hear it or sometimes it is nonexistent. ON youtube there is some kid with a stock series 3 and he puts on K&N air filter and that thing whines so loud. I have full headers, HAI, 1.9 rockers and it sounds nothing like his. Why can't I hear her whine?

Just for your sake...pull off the blower and see if the gasket moved or something...worth a shot...sounds like something underneath isn't quite sealing idk...

take a picture. the thing on the top of the blower should have all the lines filled. here, look at mine:



there is one that goes to the BBV, one that goes to the brake booster, and another that im not sure where it goes to, but i can check it a little later if need be.

Originally Posted by Bio248

there is one that goes to the BBV, one that goes to the brake booster, and another that im not sure where it goes to, but i can check it a little later if need be.

The third one goes to your HVAC controls.

If you cap the booster line and the issue goes away, your problem will be somewhere in that direction. Might want to see about getting another brake booster hose. They're cheap. Yours may have a small split.