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  1. #1
    Bill Rumble
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    Stalling & rough idle

    My 93' 740iL, 220K miles, recently had a problem with rough idle and stalling (this car NEVER stalled before), check engine light on and 1213 code. Measured the fuel pressure and found it to be at 35 psi at idle. Bentley manual says it should be 51, so I replaced the regulator which is set to 3.5 BAR. New regulator installed and still 35 psi! Turns out that this is the correct pressure. 3.5 BAR = 51 PSI ABSOLUTE pressure but not GAGE pressure. Gage pressure is 35 psi. So I now have a new regulator with same problem. I then used carb cleaner to check for vacuum leaks and found a large leak on the gasket sealing the throttle body to the intake manifold. Replaced the gasket and it now runs fine. For a reference point for the future, I measured the intake manifold vacuum and found it to be 17.5" at idle and the fuel pressure is 30 PSI (gage) at idle. The fuel pressure will go up when engine is throttled up...FIXED and running smooth again!

    FYI, ABSOLUTE pressure is measured relative to a vacuum, GAGE pressure is measured relative to atmospheric pressure.

  2. #2
    Registered Member
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    Member No: 148742 terry740 is an unknown quantity at this point terry740's Avatar
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    Jan 2007
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    Re: Stalling & rough idle

    Good info. Thanks. I recently had poor idle, rough running and after lengthy process by indy, it ended up being a poor fuel pump! He said he measured 35 psi (I don't know what method) and that it should be over 50.

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