Thread: Bad brake booster?

I have had this problem for a little while. When I come to a stop hitting the breaks my RPMs and Volts drop way down. It seems to only happen when I have my heater on high but it could just be a coincidence.

I was thinking the brake booster might be bad. Any suggestions?

I think that's normal. When you come to a stop or hit the brakes, your engine is idling in gear, aka the lowest idle speed in any table typically. Then at the same time, your engine vacuum is being used by the booster (properly and normal) to assist with the brakes. This use of vacuum can bring your rpm just a little lower.

At low engine rpm your alternator output is low. Plus.. if you get below IIRC 600rpm your pcm tells your alternator to stop working.

There are three ways you could combat this issue as I see:
1. Overdrive pulley on alt
2. Program (DHP) the alt not to turn off if you are getting below 600rpm
3. Bring your in gear idle up a 100 rpm

heck..let's toss on a 4th
4. Ensure all your cables are good and corrosion free.

How about the IAC (Idle Air Control valve). Won't that cause the RPM's to drop too low if it's not able to compensate quick enough? Think I'm having the same issue on my Honda. Idle's at normal RPM but when hitting the brakes, initially putting it in gear, or turning on the headlights it drops RPMs and the headlights dim. I just haven't got around to cleaning and lubing the stupid thing. I know it's not normal cause my other Honda with the same engine doesn't do it. Different car, but seems like the same problem. Does your RPMs surge higher than idle afterwards? Bill's 4th idea about the cable connections is a another good possibility.

The other night I did the big 3 with 4 gauge wire and a new Optima yellow top and I am still having the problem. I don't think it has to do with the battery but I guess it could be the alternator. I have a lifetime warranty on the alternator at the junk yard I bought it from so I might just swap it out.

The other thing I just noticed is when I shut the car off I can here air leak from the break booster area. I might have heard it before but but is that normal to hear from the break booster right after the car is shut off?

I might have to try and clean my IAC or put the other one I have in and see what happens.

EDIT-

It could be my alternator cutout or idle settings but even if I revert them to stock the problem still happens.