I have a 2013 Mazda 3 with 85,000 miles. Recently, my car has been idling rough - but only when I depress the brake pedal. As soon as I take my foot off the brake, it idles just fine. And If I pull up the parking brake, the car starts idling normally. The brakes have about 15,000 miles on them. They stop the car just fine and they aren’t making any noise. Any thoughts on what might be wrong?
Mazda3 Rough idle when brake pedal is pressed
- Thread starter Melissa123
- Start date
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- Pueblo county CO
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- CX-5 Sport 16.5 6M
How many miles?
It might be the brake booster. A crack that opens when you press the brake.
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- San Diego, CA
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- 2014 Mazda3 S GT auto, 2008 MX5 6-speed
I haven't seen anyone else with 2010-2013 having that problem. My 1989 MX6 GT was 25 years old when I sold it and it had never had a leaking brake booster.
By all means though you should have it checked. It could be a vacuum line that popped off its fitting.
By all means though you should have it checked. It could be a vacuum line that popped off its fitting.
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Our CX-9 had a TSB for failure of the brake booster. When it started going out, it would make hissing noises during braking. Then, when it finally let go, would cause the idle to fluctuate when pressing the brake pedal, and made stopping the car an exercise in leg strength.
While a failure of the brake booster is not common with newer cars, it can still happen.
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- 2008 Mazda5 GT
+1
unlikely brake booster but anything is possible.
Test brake booster by turning car off and pumping the brake pedal rapidly 4-5 times. The pedal will sink and stay down if there is no leak. Turn on car, pedals come back up, listen down there for any hissing (air leak). While idling in Park or Drive, pump the brake pedal rapidly 4-5 times to see if the tach jumps all over.
-Is the idle (in Drive with drivetrain engaged) normal when the car is cold (you'll get a high idle until the car warms up). Once the car is warm, the rough idle occurs?
-When it does idle rough, does it go away if you shift to Neutral (drivetrain disengaged)?
If yes, I suspect your torque converter has an internal leak/damage and not holding pressure.
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