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E46 Xi Forum
The E46 XI was produced from 01-05 in sedan and touring body styles. Powered by either a 2.5L inline 6 in the 325xi or a 3.0L inline 6 330xi. Discuss all thing about BMW AWD E46 'Xi' here.

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Old 10-25-2012, 07:37 PM   #1
SharkmanBMW
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Weird idle, normal then dips for a second - alternates a few times per minute

Likely not Xi specific, but i lik you guys

Its not really LOW rpm, maybe 50 rpm lower, but there is a noticeable change - something seems to be switching on causing a dip for a second.

Needle dips briefly and you can feel the change,

During The rough' stage, if I turn the steering it stresses it & drops a bit more.
It seems to alternate between normal rpm and dips low a few times a minute.
Car runs fine other than this.

Suggestions appreciated
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Old 10-26-2012, 10:03 AM   #2
GSherbs
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search for posts by jfoj and follow his signature links... he has a laundry list of "rough idle" causes that you can investigate.
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Old 10-26-2012, 12:21 PM   #3
SharkmanBMW
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Update. (And thanks for the reply.)

I'm sitting in the car now, and it really is something switching on & off
I hear a click then it dips briefly
I also get the occasional slight rattle of the engine or bushings when it dips.

It seems to not do it as much if I shut off the fan completely. So maybe it has to do with accessory power...
Just tried this:
If I turn on lights & heated seats I get similar result. Add fan on and it's even worse. Turning steering a lot when stationary does the same.

Again, to clarify - the idle is not rough, just a bit low.

Thanks
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Old 10-26-2012, 12:55 PM   #4
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Is your fan clutch malfunctioning? Every time you turn on headlights, seats, etc the alternator load increases and your car idle dips because of the increased load. That's completely normal. Ditto for the steering, the power steering pump uses engine power. Increase load, idle speed will dip.

Last edited by SamDoe1; 10-26-2012 at 12:56 PM.
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Old 10-28-2012, 03:53 PM   #5
Chilton88
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VANOS...it's not really a bad DIY. However, I would also clean out the Intake Solenoid cylinders and remove all the drain plugs in the VANOS housing and wash out the entire thing. I would remove all the Solenoids and clean out the Solenoid cylinders as well and then replace them.
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Old 10-29-2012, 06:16 AM   #6
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A/C cycling on and off will draw more power but in Montreal maybe not your issue now. Radiator cooling fan will cycle on and off as well. This may be an indication of a battery charging issue. Your battery and or alternator/voltage regulator may be weak
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Old 10-29-2012, 11:03 AM   #7
SharkmanBMW
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Thanks guys.

No AC being used these days lol
(People are already installing winter tires around here!)

I'll look into the vanos / fan clutch / alternator scenario.
Those have never been changed for sure, so both could use a checkup for sure!

Battery is not more than 2 yrs old, top quality, overkill battery too. Alternator is original. I'll set it on trickle charge or a day just to see if it changes anything.

Much appreciated
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Last edited by SharkmanBMW; 10-29-2012 at 11:08 AM.
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Old 10-30-2012, 02:10 AM   #8
Chilton88
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Consider cleaning out the intake solenoid cylinder first and also cleaning your intake camshaft position sensor while you're there. You would need a 32 mm open wrench for the solenoid, which you would use for the fan clutch.
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Old 11-01-2012, 12:27 AM   #9
White_Knuckles
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The A/C does cycle on in heat/defrost mode. Even when my car is switched over to winter mode, I've heard the A/C compressor click on. It's used to "dry" the air. It only runs briefly but will tug on the motor. Turn your HVAC controls completely off and test for the sound or lag.
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Old 11-04-2012, 09:51 AM   #10
SharkmanBMW
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Yellow oil light came on after posting this, I added 1 litre (quart) and its much better...
So, how/why would low oil / oil pressure cause that?!
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