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Discussion Starter #1
Once the car warms up it randomly runs rough at idle at lights. It becomes more noticeable as I pull away in first.

Oddly, if I slowly rev it up the roughness instantly vanishes once I hit ~2200rpms, and then it will idle smooth as silk again.

Car does not throw ses light.

I theorise something in the vanos is sticking, any one confirm???
 

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Not having an SES does not mean that the car isnt throwing codes, though. Check them just in case (good weekly routine, actually).
 

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If it hasn't tripped the light yet, it probably will soon. Do a scan and you may get some hints as to the issue.

Dave
 

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Once the car warms up it randomly runs rough at idle at lights. It becomes more noticeable as I pull away in first.

Oddly, if I slowly rev it up the roughness instantly vanishes once I hit ~2200rpms, and then it will idle smooth as silk again.

Car does not throw ses light.

I theorise something in the vanos is sticking, any one confirm???
Does anyone know if something happens around 2200 rpm? For example does the car run on the idle circuit and around 2200 the car blends in the throttle bodies themselves? Or is the car open loop until that rpm ? (these are just illustrations, not facts!)

If there is some type of changeover around that rpm, then perhaps we can help diagnose it, assuming codes don't reveal a problem.
Regards,
Jerry
 

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under 2200

Just a guess, but how about that is when the secondary air system is running?

ssomed
 

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Discussion Starter #6 (Edited)
Ok so since I originally posted this thread I've taken it to a good indy shop and they scanned it; it's not throwing any codes. I replaced the vent hoses and cleaned the oil seperators, no improvement.

Occasionally the car runs extreemly rough below ~2200 rpms, massive loss in power and a stumbling surging feeling. Feels like a cylinder is missing and the lack of a fault code astounds me. As soon as you get it over ~2200 rpms the stumbling vanishes instantly and then is gone and the car runs super smooth in the low revs.

I'm stumped. My shop (been in the BMW game for many years) is stumped. The thought that I might have to live with this makes me sick.

edit: the amount of stumbling seems to vary, sometimes it is barely noticeable....
 

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Ok so since I originally posted this thread I've taken it to a good indy shop and they scanned it; it's not throwing any codes. I replaced the vent hoses and cleaned the oil seperators, no improvement.

Occasionally the car runs extreemly rough below ~2200 rpms, massive loss in power and a stumbling surging feeling. Feels like a cylinder is missing and the lack of a fault code astounds me. As soon as you get it over ~2200 rpms the stumbling vanishes instantly and then is gone and the car runs super smooth in the low revs.

I'm stumped. My shop (been in the BMW game for many years) is stumped. The thought that I might have to live with this makes me sick.

edit: the amount of stumbling seems to vary, sometimes it is barely noticeable....
did you check the spark plugs?
 

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Could be a vacuum leak.
 

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CPS? my symptoms were most noticeable around 2200-2500.
 

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Ok so since I originally posted this thread I've taken it to a good indy shop and they scanned it; it's not throwing any codes. I replaced the vent hoses and cleaned the oil seperators, no improvement.

Occasionally the car runs extreemly rough below ~2200 rpms, massive loss in power and a stumbling surging feeling. Feels like a cylinder is missing and the lack of a fault code astounds me. As soon as you get it over ~2200 rpms the stumbling vanishes instantly and then is gone and the car runs super smooth in the low revs.

I'm stumped. My shop (been in the BMW game for many years) is stumped. The thought that I might have to live with this makes me sick.

edit: the amount of stumbling seems to vary, sometimes it is barely noticeable....
From the dark recesses of (an admittedly overworked) brain, I remember reading in some discussion (D/A?) that the throttles work off the idle circuit up to a certain rpm (2200??). Then, the throttle bodies take over. I may be off here, but check with some of the real gurus with hands on tuning experience to confirm that. A PM to some of them might provide some insight.

If not, then the only thing that comes to mind is throttle bodies that are sticking, so they are out of sync occassionally. Have you tried a thorough TB clean??
Regards,
Jerry
 

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I have a similar issue. However, I noticed a had a ripped vacuum tube on the driver's side. Repaired vacuum leak, issue still there.
 

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I had the same issue on my '01 M5. There were no fault codes and 2 dealers couldn't find the fault. But my local independent mechanic diagnosed a faulty fan clutch. It was sticking and causing vibrations through the car which sounded and felt just like a misfire. It would disapear when i revved the car as the fan clutch free wheels at about 3000 RPM. The way to chech is have someone stop your fan with a newspaper (take precautions here!) whilst you rev the car, if this stops the vibration it is a bad clutch. Replacement cost me approx £150 and totally cured the problem.
 

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i have a friend that is haveing the same issue with his car im going to look at it tonight with the gt1 so far the basic items that the m5 eats have been changed spark plugs coilends purge valve mafs, im starting to think it maybe a cps starting to go south
 

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Discussion Starter #14
I had the same issue on my '01 M5. There were no fault codes and 2 dealers couldn't find the fault. But my local independent mechanic diagnosed a faulty fan clutch. It was sticking and causing vibrations through the car which sounded and felt just like a misfire. It would disapear when i revved the car as the fan clutch free wheels at about 3000 RPM. The way to chech is have someone stop your fan with a newspaper (take precautions here!) whilst you rev the car, if this stops the vibration it is a bad clutch. Replacement cost me approx £150 and totally cured the problem.

Interesting I'll have to explore that avenue thanks for the info.
 

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Discussion Starter #15
i have a friend that is haveing the same issue with his car im going to look at it tonight with the gt1 so far the basic items that the m5 eats have been changed spark plugs coilends purge valve mafs, im starting to think it maybe a cps starting to go south
Cool keep us posted.
 

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Could be MAFS as well if they haven't been replaced recently. Dirty MAFS will cause rough idle at low rpm without tripping any codes.
 

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ok so when i cked out my firends car it had no codes stored. so we scoped it and ran the vanos test it failed intake on bank one 12% leak and exhaust on bank two had 5% leak. we were shocked there were no codes as of now we are stumped he has been running 5 w30 bmw oil so i thought ok if the seals are leaking in the vonos unit we can comfirm bad vanos units by changeing the oil to 10 w 60 since its thinker if there is an improvement we know its the seals in the vanos unit, well that didnt show us any signs of improvement so know we ordered 4 cps and the car only has 40k and is not a beat on car
 
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