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Old 01-21-2013, 12:40 PM   #1
hemi_fan
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2002 325is Idle Surge and Oil Consumption

My brother's 2002 325is with approximately 190,000km has an occasional idle surge during which the idle will oscillate up and down more and more until the vehicle stalls or until you push the gas. It doesn't do this all the time and from what he's told me it is usually when he's slowing to a stop but I've experienced it just moving the car out of the driveway. Last summer we did the usual ICV cleaning (it was already pretty clean), checked for vacuum leaks, etc. but didn't find anything.

His car also consumes quite a bit of oil. I'd say probably around 1L/1000km. I'm not sure what the common causes of oil consumption are on an e46 so I haven't looked into it for him (although I like to brag that my 1999 323is with similar mileage idles fine and burns no oil at all haha).

Any suggestions on troubleshooting the surging idle? And are there any common, repairable reasons for oil consumption?
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Old 01-21-2013, 03:09 PM   #2
ac_2007
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Surge is likely a vacuum leak, perhaps check the lower intake boot for cracks first (rubber intake hose leading to idle control valve).
The bouncing idle is also attributable to a faulty/dirty MAF, failing crankcase vent, and bad voltage regulator on the alternator.

Common oil consumption source seems to be the valve cover gasket.
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Old 01-21-2013, 03:36 PM   #3
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We previously looked for vacuum leaks and found none. We also cleaned the MAF, DISA, and ICV but it made no difference.

I will have to look into the valve cover gasket. The car does not leak oil externally, would the gasket cause it to leak into the cylinder and burn?
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Old 01-21-2013, 04:25 PM   #4
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If the leak is not external, it likely won’t be the VCG. You could always use a foaming degreaser in the engine bay to clean absolutely everything, and then keep looking for seepage.

Internally, the common issue would be the CCV – crankcase vent. Oil gets in the intake and you essentially burn it off.
Other than that, you’re looking at valve guides/seals or worn out piston rings (less likely – but depends on mileage)

Double check the CCV; if the issue persists and since this is probably an older/higher mileage vehicle – add 1L Lucas Oil Stabilizer with the oil (replaces 1L, not adding 1L over max oil level).
That stuff is like molasses, and should at least help slow the burn. Plus it offers protection on cold starts, since its essentially engine assembly oil.
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Old 01-22-2013, 02:53 AM   #5
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Surging could be a failing fuel pump. If it hasn't been replaced, then it's definitely due for failure.
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