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IAC valve vacuum hoses on M20B27

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    IAC valve vacuum hoses on M20B27

    Was trying to figure out where the IAC valve was on my engine, and I found out that it is on the intake runner that feeds the rearmost cylinder and has a whole bunch of vacuum hoses that snake over the intake manifold. WTF were they thinking with this setup??? This is the most convoluted IAC valve setup I've seen on an engine - so many potential vacuum leaks waiting to happen. Also makes valve adjustments a PITA since there is so much stuff that needs to be taken off.

    Here is the M20B27 IAC valve setup (not my car, but similar):

    Click image for larger version  Name:	7351550198_fc9ece49e7_b.jpg Views:	13 Size:	74.7 KB ID:	9882694

    Found out that the M20B25 has a much simpler setup that hooks up the valve straight from the intake boot to the intake manifold. Here is the M20B25 setup:

    Click image for larger version  Name:	M20B25 intake.jpg Views:	11 Size:	78.7 KB ID:	9882695

    Would I be able to convert my M20B27 IAC valve setup to the M20B25 IAC valve setup while retaining the B27 intake manifold and valve cover?
    Last edited by ZeKahr; 11-03-2019, 09:53 AM. Reason: Added clarifications

    #2
    dont you need an "i" head for that switch up?? that looks to be an eta. i could be wrong. sent from hell using tapatalk
    ~~~~~~~~~~~~~~~~~
    '90 325i sedan daily driven
    '85 325e coupe also a daily

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      #3
      Originally posted by cheffy30 View Post
      dont you need an "i" head for that switch up?? that looks to be an eta. i could be wrong. sent from hell using tapatalk
      The top pic is an Eta setup and the bottom pic is of an i; I posted both for comparison. What I am trying to do is simplify the vacuum lines on my car, not convert over to a B25 head and intake. The M20B25 vacuum system seems a LOT simpler than the M20B27 one. I am guessing this is because of the advances made in Motronic 1.3 on the i engines vs Motronic 1.0 on the Eta engines and BMW learning from their own mistakes.

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        #4
        No, you can't, not without converting to the B25 manifold. BMW designed it that way for a reason - just leave it the way it is.
        Autobahn Motorsport - Portland, Oregon
        @autobahnmotorsport
        '88 M5 | '88 325i | '88 325is | '88 330is | '91 325is | '91 M-Technic 325ic | '93 740il | '03 325it

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          #5
          you should be able to as long as all sensors are reading correctly.. a 1988 SETA will have all the new setup but its also 1.3 ECU/wiring setup

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            #6
            The ETA uses a separate module to control the idle as opposed to 325i and SETA being controlled by the ecu. Leave it as is.
            '85 Alpine Weiß 2-door with m20b30 ground up build

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