R56 Flutter while under load / Vacuum leak?
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1st Gear
Joined: Aug 2025
Posts: 19
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Flutter while under load / Vacuum leak?
Hello.
R56 MCS 2009 N14
First of all, absolutely no related codes are present... The car DOES sometimes go into limp mode, but not every time. All hoses leading to the turbo, air intake, cabin vent, and the hoses on the passenger side of the car (Left hand drive) are tight and secured.
The car drives absolutely fine, but the moment that boost would normally kick in, you can sort of "feel" and absolutely hear, the turbo/boost flutter, it technically has boost, but the moment you try to step on the gas, it just flutters so it gains no power. If you slowly speed up with the car, it will go as fast as you'd like, but the boost is not there. I have a short video that might help out. Reminder, this ONLY happens under load... You cannot repeat this while "driving" on the lift, this has been attempted, theres no good way to be up under the hood while its happening.
It had no issues, no air leaks, perfect boost until it was parked last year in September, it was parked most of the time indoors, but always on concrete the entire winter. Took it apart to re-do the subframe, and replace/upgrade bushings, install coilovers etc, now when its back together were seeing this air leak. :(
- Upgraded Wagner intercooler installed (Stole it off the 2008 MCS), did not test the 2008 beforehand, it had a misfire on cylinder 2 which wasn't diagnosed, so wasn't running properly beforehand unfortunately.
- Milltek cat-less stainless steel exhaust system, though probably irrelevant for this problem.
- Milltek cat-less downpipe
(The car ran fine with these upgrades for 5-6 months while driving regularly last year)
I have another R56 which is an 2008 MCS, and the same problem occurs, on that car I did have an Unmetered air code that I could not get rid of for the longest time, I do believe replacing the MAP sensor on that car did alleviate the code, but the boost/vacuum leak was still occurring.
Thank you!
EDIT: I uploaded the video to youtube instead of sharing the video file.
R56 MCS 2009 N14
First of all, absolutely no related codes are present... The car DOES sometimes go into limp mode, but not every time. All hoses leading to the turbo, air intake, cabin vent, and the hoses on the passenger side of the car (Left hand drive) are tight and secured.
The car drives absolutely fine, but the moment that boost would normally kick in, you can sort of "feel" and absolutely hear, the turbo/boost flutter, it technically has boost, but the moment you try to step on the gas, it just flutters so it gains no power. If you slowly speed up with the car, it will go as fast as you'd like, but the boost is not there. I have a short video that might help out. Reminder, this ONLY happens under load... You cannot repeat this while "driving" on the lift, this has been attempted, theres no good way to be up under the hood while its happening.
It had no issues, no air leaks, perfect boost until it was parked last year in September, it was parked most of the time indoors, but always on concrete the entire winter. Took it apart to re-do the subframe, and replace/upgrade bushings, install coilovers etc, now when its back together were seeing this air leak. :(
- Upgraded Wagner intercooler installed (Stole it off the 2008 MCS), did not test the 2008 beforehand, it had a misfire on cylinder 2 which wasn't diagnosed, so wasn't running properly beforehand unfortunately.
- Milltek cat-less stainless steel exhaust system, though probably irrelevant for this problem.
- Milltek cat-less downpipe
(The car ran fine with these upgrades for 5-6 months while driving regularly last year)
I have another R56 which is an 2008 MCS, and the same problem occurs, on that car I did have an Unmetered air code that I could not get rid of for the longest time, I do believe replacing the MAP sensor on that car did alleviate the code, but the boost/vacuum leak was still occurring.
Thank you!
EDIT: I uploaded the video to youtube instead of sharing the video file.
Last edited by WaFFlz; Today at 07:47 AM.
3rd Gear
Joined: Dec 2022
Posts: 200
Likes: 51
From: Rutland, VT
It definitely sounds like a small leak somewhere.
I would spray water (will drop rpm) or start fluid (rpm will rise) around every line/hose to find any possible cracks/leaks. I added small/thin zip ties to help seal all these lines. Clean MAF/MAP sensors. Check fuel pressure!
Then Id check and see if its the Diverter valve causing the issue.
I would spray water (will drop rpm) or start fluid (rpm will rise) around every line/hose to find any possible cracks/leaks. I added small/thin zip ties to help seal all these lines. Clean MAF/MAP sensors. Check fuel pressure!
Then Id check and see if its the Diverter valve causing the issue.
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