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Hi guys I need some help/opinions. Just bought an 2009 M5 with 70K miles, I noticed that after the vehicle is warmed up, when I shut off the vehicle and restart it, the idle will surge between 600-900 RPM until I drive it. Then it idles perfect until the next warm start. Cold start it's fine no surges. Brought it in to the dealer and they say it's normal for a V10 to surge. No fault codes in any modules. I only have full RPI exhaust for mods. I have seen it on an 06 M5 but not as bad as mine. Any thoughts on what it could be or is it normal? Thanks in advance.
 

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Yes. I've had this for a long time - most notably after filling up with gas. And, my vanos solenoids are testing bad and I am pretty sure that's what's causing it. Troy's comment just nailed it for me. I'll replace mine when they get here next week and let you know if it's fixed. Dealer told me it's normal too, which definitely is not the case.
 

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I tripped up on this sensor last week looking around the internet. A lot of people seem to have this bouncing idle issue. Mine is smooth as silk hot or cold, but would try this part if it did bounce. It's in the vacuum system. Cheap enough to try. I haven't seen anyone really solve this bouncing idle but I also I haven't seen this part mentioned either. Look what ECS tuning says about it. It's worth a try IMO.

Search SiteSearch 13628617097 - 13628617097 - Pressure Differential Sensor - ES#2641334

Here is the part location, it's #2:http://www.realoem.com/bmw/showparts.do?model=NB93&mospid=48807&btnr=11_3710&hg=11&fg=45
 

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I tripped up on this sensor last week looking around the internet. A lot of people seem to have this bouncing idle issue. Mine is smooth as silk hot or cold, but would try this part if it did bounce. It's in the vacuum system. Cheap enough to try. I haven't seen anyone really solve this bouncing idle but I also I haven't seen this part mentioned either. Look what ECS tuning says about it. It's worth a try IMO.

Search SiteSearch 13628617097 - 13628617097 - Pressure Differential Sensor - ES#2641334

Here is the part location, it's #2:RealOEM.com Â* BMW E60 M5 Vacuum control - engine
thanks. ordering one now.
Interesting!! I never heard or seen that part before on our cars! Nice find capt!

Tbrown, cant wait to hear if this has changed or helped! I would be next online for this and this would be big!

a few guys thought the charcoal filter was to blame for this, i changed and cleaned the components to the charcoal filter to no avail. This sounds closer to a fix then that did. I would think if the sensor was bad, it would be bad constantly? Not just on warm starts?
 

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Interesting!! I never heard or seen that part before on our cars! Nice find capt!

Tbrown, cant wait to hear if this has changed or helped! I would be next online for this and this would be big!

a few guys thought the charcoal filter was to blame for this, i changed and cleaned the components to the charcoal filter to no avail. This sounds closer to a fix then that did. I would think if the sensor was bad, it would be bad constantly? Not just on warm starts?
Just delete your charcoal filters at this point, one less thing to worry about and Euro models don't come with these silly filters :cool:
 

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A test module is provided in ISTA/GT1 for the electric vacuum
pump. The differential pressure sensor on the brake booster is
used for the purpose of monitoring the pump.
The plausibility is checked by the pressure difference between the
vacuum and ambient pressure calculated internally in the ECM. It
is evaluated and, in the case of fault, shown in the instrument cluster
and displayed as a CC message (check control).
If the electric vacuum pump is found to be defective during the
self-diagnosis procedure, the safety concept manager (SK manager)
intervenes and shuts down cylinder bank II (Cylinders 6-10).
The smaller opening cross section in the intake duct of cylinder
bank 6-10 thus ensures adequate vacuum in the brake booster.
In the case of fault the safety concept manager triggers an "engine"
symbol as well as a CC message (check control) "engine malfunction/
power loss" in the instrument cluster.

Maybe a faulty sensor could mimic a vacuum leak? I'll know in a few days.
 

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Vacuum Pump
Although the S85 does not use Valvetronic, the assistance of an
external vacuum pump is required under various operating conditions.
In some operating modes, especially with a cold engine,
when the catalyst heating function is active there is insufficient partial
engine vacuum available for brake power assistance. There is
also reduced engine vacuum when using “race track” (M-Dynamic)
mode or when the vehicle is rolling with KL15 on and the engine
off.
To make up for this limited vacuum period, there is a supplemental
electric vacuum pump. The electric vacuum pump(2) is controlled
via the ECM (DME). The pump is installed on the left in the engine
compartment under the left microfilter housing.
The vacuum pump is designed as a vane-type pump. The prevailing
partial vacuum is measured by a partial vacuum sensor.
The vacuum pump is switched on at -250 mbar and switched off
at -600 mbar.
An external pressure sensor (1), signals the pressure difference
from the brake booster compared to the ambient pressure from the
internal ambient pressure sensor in the ECM (DME). (See diagram
on the next page)
When vacuum is required, the ECM activates the relay which in
turn then actuates the electric vacuum pump. The cut-in and cutout
thresholds are controlled as a function of the differential pressure
and the vehicle speed.
The software in the ECM is configured such that the correct vacuum
is available in the brake booster under all driving conditions.
With relatively little vacuum in the brake booster, the engine must
be running or the vehicle must be rolling with terminal 15 on in
order to activate the electric vacuum pump.

I'm going to run the test procedure in DIS this weekend and see what I get.
 

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Discussion Starter #13
Thanks guys for all the reply! I'm leaning towards those solenoids too. But who can come up with the right fix they will be the winner :)
 

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I had some surging on cold starts a few times 2 weeks ago. It stopped when I started driving or waited while idling long enough (warming up). In the meantime I took a couple long (100 mi.) rides. Now it is gone, or so it seems. Subscribing to this thread just in case something useful comes out of it and the problem returns (as it usually does when you don't root cause it).
 

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I had a similar problem with mine - although it was more that the rpm would intermittently drop very low and return to normal while idling. This was when the engine was warm.

I cleaned both the MAF sensors with carb/intake cleaner and it's been fine since.
 

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What does "surging" mean ?

Mine when warm and idling the RPM goes up a then drops back down. I noticed she does this when the fan comes on. Wonder if it isn't to supply more power for engine cooling
 
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