High vacuum, rough idle [Archive] - Bimmerfest - BMW Forums

: High vacuum, rough idle

07-13-2010, 11:01 AM
Upon (cold) startup I have a rough idle on my 745i (V8 N62, 2002), but when fully warmed up it doesn't go away. Driving is ok, but with transmission in D and slowly starting to run (but keeping brakes slightly applied), you can feel the car shudder / bucking. When there's enough speed, no problems whatsoever.

I first thought this was related to the only error present in the fault memory regarding Vanos. But it's not, I can now fully reproduce the situation every time I want:

I discovered that if I start the engine when cold, and I pull the dipstick or remove the oil cap there is a REALLY high vacuum present (if I cover the oil cap opening with my hand there's a huge amount of suction). You can also hear (howling) noises in the manifold. The engine almost dies but just keeps on going,

Funny thing though is later (with the engine warmed up, be it 10km or 100km, the rough idle and high vacuum are still present) if I then stop the engine and start it again right away, the idle is 100% smooth and ok. Now if I pull the dipstick or remove the oil cap there is a REALLY low vacuum present (much less suction). And no noises in the manifold (just a little change in rpm).

So: what actual changes the vacuum pressure (from high upon startup to low when warm) and refuses to "switch" to the low setting?

I have thought of the following:
- CCV -> checked them, they are not broke, and they are mechanical and therfor not influenced by starting/stopping the engine?
- Vacuum pump -> but it's mechanical and therefor not influenced by starting/stopping the engine (and not connected to the manifold, only to the brake booster)?
- Throttebody -> but should through a code when in failure, plus would put the valvetronic in limp-home mode (how to check though???). I can hear the valvetronic motors kick in after 1 minute, so I guess no limp-home???
- Differential pressure sensor in the manifold?
- Tank ventilation valve?
- or??

Any thoughts are deeply appreciated. Although the car drives without a problem, this is driving me nuts!

07-13-2010, 02:34 PM
Sounds like you have a vacuum leaks somewhere there. Assuming vacuum means some sort of a hissing noise or something.

07-14-2010, 01:23 AM
Sounds like you have a vacuum leaks somewhere there. Assuming vacuum means some sort of a hissing noise or something.

Ah see what you mean, no with vacuum I mean underpressure which is apperent when I cover the oil opening with my hand.

07-21-2010, 01:42 AM
Ok, getting there slowly.

The GT1 tells me the valvetronic is operating in failsafe mode (see picture attached).

In that case the throttle takes over from the valvetronic to deliver air to the engine.

This causes the high(er) vacuum. Therefor the high vacuum is not the cause, but "just" a symptom.

So the (restated) problem is the following: If I start the engine when cold the engine starts and stays in failsafe mode (not just during the warm up period which is normal, but always) with rough idle.

Later (be it 10km or 200km) the rough idle and failsafe program are still present. If I then stop the engine and start it again right away, the idle is 100% smooth and ok. So no more failsafe but normal valvetronic operation.

So basically: what causes the failsafe program in the valvetronic? And (since cold startup with throttle is normal) what causes the valvetronic NOT to switch over to valvetronic operation when warmed up?

07-21-2010, 09:34 AM
Are there no errors logged in any of the areas mentioned by DIS? (in the lower-right of your screenshot)

07-22-2010, 03:06 AM
Keif, yes, only 1: 10034 (which corresponds with Peake 2732 and P0021): over advanced intake cam, bank2 (drivers side).

I have swapped the following:
- intake CPS (from Bank 2 to Bank 1)
- intake solenoid (from intake to exhaust)
- 4 coil packs (from Bank 2 to Bank 1, and while in there 8 new OEM spark plugs)

Unfortunately, the 10034 error remains on Bank 2 (and does not move to Bank 1 (or exhaust) which could have indicated faulty CPS, coil pack a/o solenoid).

The only thing remains I think is the intake VANOS unit itself, but I thought they hardly ever fail????? The VANOS resting position is retarded so I think if it's over advanced at least there is (enough) oil pressure right? Could there be something "sticking", preventing the cam to retard back??? I have also added the GT1 readout of the VANOS positions and adaptations.

Could this error force the valvetronic in failsafe mode? Could be offcourse, but why then directly back to normal operation after stopping and starting the engine again (when warmed up)?

12-10-2013, 09:20 AM
Any fix? None, anywhere that I've found, outside of selling the car.

Realizing this is an old thread, it must be more common as this generation of engines ages; like mine. I am faced with dumping the car or finding a reasonably priced fix. Other searches yield a variety of possible trouble areas, like plastic hoses.

Might this, seemingly heat-related problem be a sticky actuator or cracked vacuum hose to one?

All the computer troubleshooting is nice and helps isolate problems, but it still is an engine requiring proper delivery systems for fuel, spark and vacuum.

05-19-2014, 11:05 PM
was there any solution to this problem , my n62 has the same issues

06-11-2014, 01:00 PM
Check the "cs-adaption"

(camshaft adaptation), in INPA. It should be close to the middle (71 for exhaust, 127 for intake). Expect it is out for intake cam, according to your GT1/DIS diagnostic.

Then swap both the cam position sensor, and VANOS solenoid, for the relevant cam (intake you said?) with the other bank, see if problem stays where it is, i.e. sensors are OK.

Next, perform ram_backup in tool32 (tool32 -> open prg -> ME9_N62.prg), find highlight ram_backup -> run (f5). This will reset camshaft adaptation values. They will revert to the middle (71 for exhaust, 127 for intake). Start engine and see if cs-adaption values revert back to bad values (I read that the adaptation values can get stuck incorrectly after bad VANOS solenoid is cleaned/replaced/moved to other bank - so the ram_backup reset is the first thing to try).

If the cam shaft adaptation goes back to bad values, then probably your VANOS adjuster unit is defective, or it has slipped like mine did (http://forums.bimmerforums.com/forum/showthread.php?1826040-Timing-VANOS-1-tooth-offset-to-crankshaft&p=27687353#post27687353 ).

Re-time the cam, ensuring the vanos adjuster is set properly as part of the timing procedure, and make sure the vanos adjuster unit is bolted up tight to the cam, and see how things look then (cs-adaption).

Yes this will disable valvetronic and cause the engine to operate off the throttle, and feel lazy.

07-29-2014, 12:52 AM
I've looked after my ALPINA B5s Adaptions:

Adaption Exhaust Bank 1: 72,20
Adaption Intake Bank1: 130,50

Adaption Exhaust Bank 2: 70,50
Adaption Intake Bank 2: 126,50

I've used the "pm restore" mode and got clear 71 / 71 and 127 / 127 - but they changed to the old ones.

Is that a problem?

05-23-2015, 02:54 AM
First of all i apologize my english writing, this is not my native language.

I have maybe same fault: 2732 CDKENWS2 - NW-Steuerung Einlass Bank2
P0021 Nockenwellensteuerung Einlass (Bank 2) - Adaptionswert Spätposition unplausibel oder Leistungsproblem.

Car doesnt run or idle very well when engine is cold, there is hesitation and vibrations. Sometimes car becomes luggish during a ride when engine is warm. I think thats because valvetronic goes failsafe mode. When i turn off engine and start again car is okay most of times.

Look attachment.

-VANOS adaptation, inlet cyl 5-8 161.30 which is over limit. When i reset adaptations with tool32 this goes back to ~160 when engine is on couple of minutes.

Sometimes when i remove fault codes with example when engine is warm and drive ~20km that fault code doesnt come back immediately.


09-05-2015, 01:47 AM
Same fault still... Nowadays fault is on almost alltime, especially when engine is hot.

06-18-2016, 07:32 AM
I opened bank 2 valve cover and checked timing. Inlet camshaft timing was badly wrong. Now fault code doesnt come anymore and car runs fine.

07-11-2016, 01:47 AM
Also check for fault tolerance on the ValveTronic intermediate levers. You can do this test with INPA or with Ista/D. With ISTA/D it's just a simple yes/no result test. With INPA check the analog values of the N62's Engine module and check if there's a difference between requested and actual valve lift.

If you disconnect any of the sensors for VANOS and/or Valve Lift the valvetronic system goes into fallback mode and uses the old throttebody approach. It could be VANOS or Valve Lift. Rough idling with cold engine is usually Valve Lift and uneven filling of cylinders

07-11-2016, 01:48 AM
Do you have fully functioning ValveTronic? Or is it in degraded mode?

07-18-2016, 05:47 PM
Your alternator is running out. I had the same issue rough idle at start and when stop at the light then after I got the generator fault message. I replaced the alternator and problem gone. Also at rough idle at night turn on your lights, park the car, and look at the headlights and markers from outside while car on and if you see your headlights deeming dark and bright with the rough idle it should be your alternator. Hope this solves your problem.

03-17-2017, 11:53 PM
I opened bank 2 valve cover and checked timing. Inlet camshaft timing was badly wrong. Now fault code doesnt come anymore and car runs fine.
How did you fix it? Did you have to reposition the camshaft gear on the timing chain?

03-18-2017, 02:05 AM
How did you fix it? Did you have to reposition the camshaft gear on the timing chain?

Mechanically no the camshaft doesnt need to. I use a snap on solus ultra to set the valvetronic mark or timing mark in a sense. Scanner also guides the sequence to reset the eccentric shaft after screwing it into position. Bad eccentric shaft is a possibility if it keeps the timing off mark. Keep it simple and let the scanner guide you in sequence order and go from here.