Idle influenced by release of brake pedal

[Scrippy]

Hey everyone,

So I've been at a stop light on many occasions and felt/watched my idle fall to 500-600RPM when the day to day normal idle seems to be 750ish. When this dip in RPM occurs I've noticed that if I let off the brake on level surface (so I dont move) the RPM restores to that normal 750ish. The little knowledge I have over the whole S65 systems makes me think of a brake booster leak or vacuum leak. Do you guys have any experience/recommendations with this occurrence or a possible culprit? I'm super familiar with N54 and not so much with S65. I remember in my 335 the grommet between the brake booster and main vacuum line was a common failure. I personally changed the one on my 6 year old at the time 335 and saw an improvement on vacuum pressure. Thanx in advance!

[nick3753]

Originally Posted by Scrippy

Hey everyone,

So I've been at a stop light on many occasions and felt/watched my idle fall to 500-600RPM when the day to day normal idle seems to be 750ish. When this dip in RPM occurs I've noticed that if I let off the brake on level surface (so I dont move) the RPM restores to that normal 750ish. The little knowledge I have over the whole S65 systems makes me think of a brake booster leak or vacuum leak. Do you guys have any experience/recommendations with this occurrence or a possible culprit? I'm super familiar with N54 and not so much with S65. I remember in my 335 the grommet between the brake booster and main vacuum line was a common failure. I personally changed the one on my 6 year old at the time 335 and saw an improvement on vacuum pressure. Thanx in advance!

I have the same issue. Won't happen when the a/c is on. There was a thread a while back but not sure there was a conclusion/fix.

Edit: found it.

RPM drops on idle http://www.m3post.com/forums/showthread.php?t=681269

[Scrippy]

Originally Posted by nick3753

I have the same issue. Won't happen when the a/c is on. There was a thread a while back but not sure there was a conclusion/fix.

Edit: found it.

RPM drops on idle http://www.m3post.com/forums/showthread.php?t=681269

Thanx for the heads up. That post asks the same questions and has no answers. I'm coming to the conclusion I should just inspect my brake booster for any possible leaks. I also wonder if low pads that require a deeper brake action exacerbate things?

[Scrippy]

Repost

[KingofKingz]

This is an absolutely normal behaviour. Its due to emissions. You can also turn your steering wheel and it will go back to 750rpm. So it tries to drop rpms to decrease emissions as long as the car does not need the 250rpm more

[Scrippy]

Originally Posted by KingofKingz

This is an absolutely normal behaviour. Its due to emissions. You can also turn your steering wheel and it will go back to 750rpm. So it tries to drop rpms to decrease emissions as long as the car does not need the 250rpm more

Interesting, thank you for the info.

[bestyt]

I have exact same symptoms that after full stop, releasing brake pedal, then RPM goes down to 500 and up to 650 once. Not sure it is normal behavior.

[Scrippy]

Originally Posted by bestyt

I have exact same symptoms that after full stop, releasing brake pedal, then RPM goes down to 500 and up to 650 once. Not sure it is normal behavior.

It’s not. The dude that said that has a reputation of 18.