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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 06-05-2010, 02:14 PM   #1
antoniostarr
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pulsating idle when AC is on

When I am sitting at a light and turn on the AC the engine starts to idle erratically. I fI turn the AC it instantly begins to idle as normal. I've done a but didn't find anything specifically related to rough idle only when AC is on.

Any suggestions on fixing this?
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Old 06-05-2010, 02:31 PM   #2
Solidjake
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Do you have an automatic or an aux fan in front of the radiator? You might have a vacuum leak as well.
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Old 06-05-2010, 02:35 PM   #3
antoniostarr
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forgive me I don't know the difference between the two. It looks like this fan
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Old 06-05-2010, 02:36 PM   #4
antoniostarr
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I was thinking vacuum leak as well but after I drive with the AC for a while the pulsating stops.....
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Old 06-05-2010, 03:01 PM   #5
Solidjake
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That's an electric fan, mostly on manuals. Idk, I'd say a vacuum leak over everything else right now. I'm not really sure what else can cause it. Does the rpm drop or rise?
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Old 06-05-2010, 03:07 PM   #6
antoniostarr
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both! It goes up and down a few hundred rpms
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Old 06-07-2010, 07:47 PM   #7
325myAZ
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Could it be the Idle Control Valve?

I ask/suggest this only because I'm experiencing the same issue. The RPMs are only affected while the AC is on. Otherwise I idle fine. Sometimes while the AC is on, it drops down to 500 RPM or lower, then picks up again.

Of course it's happening now, while it's 105 here in Phoenix.
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Old 06-09-2010, 05:03 PM   #8
antoniostarr
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Quote:
Originally Posted by 325myAZ View Post
Could it be the Idle Control Valve?

I ask/suggest this only because I'm experiencing the same issue. The RPMs are only affected while the AC is on. Otherwise I idle fine. Sometimes while the AC is on, it drops down to 500 RPM or lower, then picks up again.

Of course it's happening now, while it's 105 here in Phoenix.
Thats exactly what I get! I will look into that ASAP.
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Old 06-13-2010, 03:41 PM   #9
mdrd
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my issue is when u first start up it idles roughly sometimes u have
to start it twice b4 it kicks in after few second car runs fine. Same
with the AC on idles roughly rpm goes up & down. Btw I have
06 M3 competition package with on 26k mls.
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Old 08-19-2016, 05:11 AM   #10
mike6
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Just did a search for this because I'm experiencing the same thing. Did any of you end up with a solution?
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Old 08-19-2016, 10:29 AM   #11
nutnut
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yesterday it started happening to me too
only happens when the engine is warmed up
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Old 08-20-2016, 10:03 PM   #12
ericsonp
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I had this same issue 2 months ago, 04 ZHP...it went away after I replaced the MAF with an $270 OEM one (almost everything stopped((RPM)), Tensioner Pulley, Cleaned out IAC with Carb cleaner, pulled DISA and replaced orange circular o-ring, 6 new BOSCH ignition coils, and 6 new spark plugs ....

Oh, and MAKE SURE your A/C system is FULL, a lack of FREON will case an erratic idle every time you use the A/C and the Fan will stay on HIGH also, electric version!!!
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Old 09-12-2016, 06:33 AM   #13
nutnut
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a clarification: it happens whenever the engine gets heat soaked

the AC on is unrelated
it is just more likely to be on on a hot day when also the engine can get heat soaked easily

Quote:
Originally Posted by nutnut View Post
yesterday it started happening to me too
only happens when the engine is warmed up
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Old 12-01-2016, 03:21 PM   #14
Anthr76
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I as well somewhat have this problem. It happens to me if I'm coming to a stop. The RPMs will dip and rise and you can hear a faint 'grind?' some type of noise I'm assuming coming from the compressor because it only happens when the A/C is on. It doesn't matter the temperature. I recently replaced my pulleys. I have a AUX fan
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