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Old 10th February 2011, 17:32   #1
Jakg
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Default Revs drop while braking

Wierd issue, this...

If I'm cruising along, and pop it out of gear, and start to brake, the revs obviously fall off - but rather than fall to idle (~800 RPM), it falls a bit further (~600 RPM), which makes the engine quite harsh (akin to being on the edge of stalling).

Once the car stops, the revs stay at ~600 for half a second and then it returns to normal idle.

And all of this is while out of gear

Any ideas? Car idles fine, if I pop it out of gear but let it coast it idles properly as well.
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Old 10th February 2011, 18:56   #2
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Quote:
Originally Posted by Jakg View Post
Wierd issue, this...

If I'm cruising along, and pop it out of gear, and start to brake, the revs obviously fall off - but rather than fall to idle (~800 RPM), it falls a bit further (~600 RPM), which makes the engine quite harsh (akin to being on the edge of stalling).

Once the car stops, the revs stay at ~600 for half a second and then it returns to normal idle.

And all of this is while out of gear

Any ideas? Car idles fine, if I pop it out of gear but let it coast it idles properly as well.
Why do you, 'Pop it out of gear and coast' ????

You are probably upsetting your vacuum pump by letting the revs drop and then braking which needs to use vacuum.

The decrease in vacuum upsets the calibration of the fuel input by the ECU.


Colvert.
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Old 10th February 2011, 18:58   #3
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Not really a 'Weird issue'

More like weird behavior. PMSL.
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Old 10th February 2011, 20:28   #4
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I highly doubt a loss of vacuum would cause the engines RPM to drop, when the brakes aren't connected to the engine as it's out of gear.
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Old 10th February 2011, 20:34   #5
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The vacuum brake servo is connected to both the brakes and the engine. It sounds to me like a vacuum issue.
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Old 13th February 2011, 15:04   #6
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The vacuum brake servo is connected to both the brakes and the engine. It sounds to me like a vacuum issue.
I second that.
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Old 13th February 2011, 15:15   #7
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The vacuum brake servo is connected to both the brakes and the engine. It sounds to me like a vacuum issue.

I agree
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Old 13th February 2011, 18:02   #8
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Default Revs drop while braking

My son passed his test last year, and I was eventually banned from trying to teach him myself because things have changed since I passed my test (probably about 1960)
The main thing was that changing down when approaching lights etc is frowned upon - you are told to coast and brake, hence the probable reason behind the enquiry.
I was told that brake pads are cheaper to change than clutch or gearbox.
(I still go down the gears though!)
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Old 13th February 2011, 21:29   #9
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Me too!

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Old 13th February 2011, 21:59   #10
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Quote:
Originally Posted by Jakg View Post
Wierd issue, this...

If I'm cruising along, and pop it out of gear, and start to brake, the revs obviously fall off - but rather than fall to idle (~800 RPM), it falls a bit further (~600 RPM), which makes the engine quite harsh (akin to being on the edge of stalling).

Once the car stops, the revs stay at ~600 for half a second and then it returns to normal idle.

And all of this is while out of gear

Any ideas? Car idles fine, if I pop it out of gear but let it coast it idles properly as well.
Mines is doing exactly the same and i have seen it mentioned on here before, almost like the clutch doesn't disengage properly and the car gets close to stalling as you slow down. Don't know if related or not but my master cylinder for the clutch is shot as i've bled it twice in the last couple of months and still sometimes when you over use the clutch it sticks to the floor and engine has to be switched off to get it out of gear. Just ordered a new one today another lovely job to look forward to!!
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