2012 Mazda5: Engine Revving When Brakes Applied

[dottdott]

I have a 2012 Mazda5. Periodically, I apply the brakes the engine just revs up. It started doing it a few times a month but now it's doing it more and more frequently, every time we drive it.

So my questions are:

• I guess, what the crap is it doing? Engine?
• Is this typical for this year range or year of Mazda5 car to start doing now that it's 9 years old?
• If it's engine (or other), what has been needed to be done? New engine? New __?

Any information is appreciated, thank you so much!

 

[Mazdiod2]

Could it be a vacuum leak, maybe in the vacuum booster.

 

[youri]

No not typical for that car year.

It might be mechanical in nature, but most of the time engine reving with brake application comes from hitting the gas pedal. So maybe the way you are sitting your boot is slightly hitting the gas pedal when you are braking, or something like your floor mat is interfering with the gas pedal. When wearing big boots you wouldn’t even feel the gas pedal. I would try to rule these out first. Check your footwell area to make sure there is nothing interfering and try to replicate the issue in a safe area and observing if you are hitting the gas pedal as well.

If you rule those out, then maybe try to provide a bit more detail on when it happens. Is it an automatic or manual transmission? Does it only happen in specific scenarios? (Full stop only, when decelerating on the highway, etc). Does it go all out or does it rev just a little bit, etc. With these info we might be able to pinpoint the issue a bit more.

As mazdiod2 mentioned it could also be a vaccum leak from the brake system.

 

[dottdott]

Thanks for all y'all's replies!

I'm definitely not hitting the gas pedal. It's done it too many times and I've been paying close attention to it, I know I'm not doing that. Nothing in the footwell.

It's an automatic transmission. Only happens when braking. It revs just a little bit, but enough that people that happen to be crossing the street take off running.

 

[youri]

Then I would suggest checking the brake booster vacuum leak that was mentioned above.

Does it do it when the transmission is in park (i.e. engine is running, car transmission is in park, if you release the brake and press it again, does that make the rpm change)?

 

[Silentnoise713]

Description sounds like leaking brake booster (diaphragm or seal). You can test the brake booster by disconnecting the vacuum hose (check hose also) and plug/cap it off. Start car and apply/pump brakes to see if rev change. You should be able to find Youtube vids to guide you; it is a generic process that applies to all cars.