Brakes depressed- Bad idle

[lolcantturn]

Hi I have an awkward problem. When I press on the brakes, my idle gets pretty freaking terrible. It's somewhat pretty steady normally but when I press on the brakes the idle drops and surges and then when I let go it's normal. What the hell? I bathed the motor in carb cleaner where the hose from the booster to the intake manifold meet but there is no vacuum leak. What gives ever-knowing-24v-forum of r3v?

[bimmerteck]

Sounds like a bad check valve, or a failing booster.

[801coppertop]

Check the vacuum lines from the brake booster those can affect idle. That's where I would start..

Sent from my SAMSUNG-SGH-I777 using Tapatalk

[e30rapidic]

spray a little wd-40 or similar to check for vacuum leaks in the hose or connection, then look into the check valve, then possibly booster. Boosters rarely fail though.

[ForcedFirebird]

Check valve is probably bad. Idle won't change spraying it since the leak is internal. Pull off the brake booster hose from the engine and brake booster. Air should be able to pass only towards the engine, if it can go both directions, then your engine is sucking in air from the booster when the brake pedal is depressed.

[lolcantturn]

well I pulled the booster line, and with the line from the manifold with the check valve in my hand, I can feel vacuum. Bad check valve?

My car also idles better when I have the intake manifold booster vacuum line plugged! Is this correlated to my check valve too? Perhaps my booster is bad too?Running boosterless is very scary though.

[ForcedFirebird]

No, you should feel vacuum with the engine side connected, the booster uses vacuum on a diaphragm to help the braking. Valve is bad if it allows the air to travel the other direction. Sorry of the last post was confusing.

Also check the o-ring at the booster, make sure it's still pliable.

[DaveSmed]

Here's how you test the check valve.

Shut the car off, and then try the brakes after a minute or so. You should get 2-3 assisted pumps before vacuum is depleted.

If not, the booster or valve could be suspect. Fire it up again, let it idle for a bit and then pinch the vacuum line off. Redo the same steps as above. If you still don't get your 2-3 "reserve" pumps, you prob need a booster.

Lastly, it is simply a check valve. You should be able to suck air through one side and not the other.


I'd say its the booster though if its changing how the car is running. Which sucks cause its a PITA.

[lolcantturn]

Here's how you test the check valve.

Shut the car off, and then try the brakes after a minute or so. You should get 2-3 assisted pumps before vacuum is depleted.

If not, the booster or valve could be suspect. Fire it up again, let it idle for a bit and then pinch the vacuum line off. Redo the same steps as above. If you still don't get your 2-3 "reserve" pumps, you prob need a booster.

Lastly, it is simply a check valve. You should be able to suck air through one side and not the other.


I'd say its the booster though if its changing how the car is running. Which sucks cause its a PITA.

Well I'm able to blow and suck air through the check valve.....So culprit one found.
Though I'm thinking my booster is also bad because my car idles and runs better when I have the intake manifold booster port blocked off. I didn't feel like I got my 2-3 "reserve" pumps.

[kalib0y]

sounds like vacuum problem like everyone above has stated