Ok I have a rebuilt street port 13b s4 with about 560 miles on it so far...I having problems with the idle. If I drop the idle down to around 1000 rpm the car wants to die out. Or if I turn the steering wheel it will also bog down or die on me with the rpm down to around 1000 rpms. Could this be because of the brake booster lossing vaccum??? I'm pretty sure the brake booster is bad... it makes a loud whistle sound and the brake pedal gets alittle stiff when hitting the brakes. Could someone please explain to me what might be happing when I drop the rpms down? Let me know please.

Does your car have power steering?

Sounds like the BAC valve isn't working right.

Yes I have power steering also have a/c.



How can I check to make sure if the bac valve is working properly?



Also would a bad brake booster cause a sparatic idle ?

It may not be the booster, could be the brake lights- increased electrical load + non-functional BAC= flaky idle.

Check here page F1-41.

Well I know the brake booster is bad it makes a whistle sound and its not stoping the way it should. Same thing happened with my 96 eldorado. So that's why I ask... I know the brake booster works with vaccum so wouldn't it mess with the idle???

OK, given that info, yes, the leaky booster could mess with the idle.



That doesn't explain why turning the wheel would cause the idle to drop though.

yes, bad booster will be a vacuum leak. disconnect it, plug the hose on the engine side, and see if the idle gets better



i wouldn't try to drive it, with out the power brakes, it takes a STRONG leg without it.

Well I'm looking to replace the booster today...but like clokker said it does explain why the power steering wants the car to die out.......how do I check the bac valve??

2 ways



if you hook up power and ground it should click, like an injector



the other way, with the engine warm and running, unplug it, if the idle drops, the BAC was working

Ok replaced that brake booster! Pain in the ass crack!!! But not that bad.

So the motor seemed to be idleing better after I repaced the booster plus the whistle went away.





So I droped the idle down from around 1500 to where it should be

Warmed the car up, moved the wheel, hit the brakes and moved the wheel, everything seems to be working fine.....until the mtherf*cker started with that funky idle crap again!



Here's the odd thing it seems to really want to do it when I put the car in gear!!



This little problem bets the hell out of me!!! But I'm going to check the bac valve next.



J9fd3s your right I forgot about sending power to it and listing for the click. Ill post if its not my bac valve going bad.