Technical Brake pedal hissing and stalling on idle

[Troughy]

Hello!
I've recently bought my first car, a 2013 Fiat Punto with over 215.000kms. The alternator and exhaust were replaced (used parts).
Recently while driving and braking, the pedal suddenly felt weird, I'm not sure but there might have been a sound like something fell out of the car. The brake pedal started making a hissing sound while pressing it (only while the car is stationary). At the same time it started idling rough, with the AC and radio on, it even stalled. But just turning on the lights is enough to make it start fighting. (Btw the engine did sound differently when turning on the lights even before this incident but I thought it was normal, it wasn't shaking or anything.) Based on some research I thought it could be a brake booster vacuum hose leak. My mechanic was in a hurry and showed me that his brake pedal is making the same sound (it really is) and that it's normal, and only said to take the car somewhere to have the battery/alternator tested.
My question before I take the car to another mechanic is: is my vacuum hose theory a good theory or could this be something more serious?
Thanks.

 

[bugsymike]

Hello!
I've recently bought my first car, a 2013 Fiat Punto with over 215.000kms. The alternator and exhaust were replaced (used parts).
Recently while driving and braking, the pedal suddenly felt weird, I'm not sure but there might have been a sound like something fell out of the car. The brake pedal started making a hissing sound while pressing it (only while the car is stationary). At the same time it started idling rough, with the AC and radio on, it even stalled. But just turning on the lights is enough to make it start fighting. (Btw the engine did sound differently when turning on the lights even before this incident but I thought it was normal, it wasn't shaking or anything.) Based on some research I thought it could be a brake booster vacuum hose leak. My mechanic was in a hurry and showed me that his brake pedal is making the same sound (it really is) and that it's normal, and only said to take the car somewhere to have the battery/alternator tested.
My question before I take the car to another mechanic is: is my vacuum hose theory a good theory or could this be something more serious?
Thanks.

If pressing the brake pedal makes the engine run rough then usually that does indicate a brake vacuum fault.
If brake vacuum is faulty the brake pedal will feel hard, but require more pedal pressure to stop the car.
You can test the brake servo by with engine off press the brake pedal several times, it should go hard, then with pedal pressed , start engine and pedal should go down a bit as pedal pressure becomes easier with servo vacuum operation.
Normally the brake vacuum should hold for some time after switching engine off.
If you trust your mechanic, ask him to check again when he is not so busy.
Or go to another mechanic and ask his opinion.

 

[Troughy]

If pressing the brake pedal makes the engine run rough then usually that does indicate a brake vacuum fault.
If brake vacuum is faulty the brake pedal will feel hard, but require more pedal pressure to stop the car.
You can test the brake servo by with engine off press the brake pedal several times, it should go hard, then with pedal pressed , start engine and pedal should go down a bit as pedal pressure becomes easier with servo vacuum operation.
Normally the brake vacuum should hold for some time after switching engine off.
If you trust your mechanic, ask him to check again when he is not so busy.
Or go to another mechanic and ask his opinion.

I did the test you mentioned and it did go down when starting the engine. The pedal didn't become harder, it actually might have become a little bit easier to press (or with less pedal force I get more braking). Also the brake pedal doesn't have to be pressed for the idle to be rough. I will take it to another mechanic, just wanted to ask here first, in case someone has experienced the same issue.