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Thread: Warm Start RPM Stumble

  1. #1

    Warm Start RPM Stumble

    I'm having this weird issue when I start the engine when it is warm and the rpms will stumble. I need to give it a little gas to get the revs up and then it will idle normally.

    Cold starts however are normal.... Can anybody think of a cause for this?

    Thanks!

  2. #2
    Join Date
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    I would bet you a cold beer that you have an injector that leaks down when the fuel rail is pressurized and car is off.
    My car has this EXACT failure mode and I have a new injector arriving today.

    here is a thread to cross reference... Leaky Fuel Injector

    Name:  E46m54b30InjectorLeak.jpg
Views: 86
Size:  283.2 KB

    BMW CCA # 510252

  3. #3
    Join Date
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    A+ diagnostics work!


  4. #4
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    Seeing those injectors makes me want to pull my fuel injection rail and inspect them! I have to do that anyway to remove the intake manifold so I can replace a coolant pipe (been on my to-do list for many months).

    I have had a warm-start stumble for a while though it seems to happen less frequently recently. The engine shakes but does not seem to be misfiring. Revving it or pushing in the clutch pedal eliminates the shaking, and it also goes away on its own after 10-20 seconds. Assumed it was a flywheel problem, but now wondering if it could be dirty or leaky injectors.

  5. #5
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    Quote Originally Posted by ryankokesh View Post
    A+ diagnostics work!
    Thanks!!!

    Quote Originally Posted by LivesNearCostco View Post
    Seeing those injectors makes me want to pull my fuel injection rail and inspect them! I have to do that anyway to remove the intake manifold so I can replace a coolant pipe (been on my to-do list for many months).

    I have had a warm-start stumble for a while though it seems to happen less frequently recently. The engine shakes but does not seem to be misfiring. Revving it or pushing in the clutch pedal eliminates the shaking, and it also goes away on its own after 10-20 seconds. Assumed it was a flywheel problem, but now wondering if it could be dirty or leaky injectors.
    What you are describing are the other characteristics of the issue!
    Its really not hard at all to check them.

    BMW CCA # 510252

  6. #6
    Thanks! What's the difficulty of a DIY? I replaced the water pump myself a couple months ago, easier or tougher than that job?

  7. #7
    Join Date
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    The one circled in red does not look like the one with the clean tip?

    "No flamesuit required"
    "Flame suit NOT REQUIRED!!!"
    Call Me Dane l 2/2004 330i ZHP l 18x8 ET45 BBS CK's wrapped with Michelin Pilot Sport AS3+ @ 245-40-18 l KW V1 Coilovers in front l KW V1 springs w/ Bilstein B8 dampeners in rear l BMW Performance Rotors l UUC StrutBarbarian l Racing Dynamics Rear Strut Bar l Jim Conforti Shark Injector l Light Birch Interior Trim l Bimmian Celly Mount l M3 Trunk Mat l l e90 Performance E-Brake & Shift Knob l M3 Tri-Stitched Boots l AL Headlight Retrofit with ZKW Lenses l CobyWheel Wrap w/M3 Stitching l LCM sw 4.5 triple blink and rear fogs

  8. #8
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    Quote Originally Posted by dml5055 View Post
    Thanks! What's the difficulty of a DIY? I replaced the water pump myself a couple months ago, easier or tougher than that job?
    It is easier than water pump, I'd say. Definitely less time. No special tools needed. The closest thing to special would be the torx I used to remove the cabin filter tray screws. Only other tools are really a 10mm socket with extension and a flat head screwdriver.
    I swapped my injector for a new VDO/Siemens unit today and it is PERFECT. SOO happy.


    Quote Originally Posted by danewilson77 View Post
    The one circled in red does not look like the one with the clean tip?

    "No flamesuit required"
    The main pic was taken just after fuel pump priming.
    Takes a little while (maybe 2 to 3 minutes) to really notice the seepage.

    The red circle is an 'after' fuel pump priming (>3 minutes).

    BMW CCA # 510252

  9. #9
    Join Date
    Jan 1970
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    Understood

    "No flamesuit required"
    "Flame suit NOT REQUIRED!!!"
    Call Me Dane l 2/2004 330i ZHP l 18x8 ET45 BBS CK's wrapped with Michelin Pilot Sport AS3+ @ 245-40-18 l KW V1 Coilovers in front l KW V1 springs w/ Bilstein B8 dampeners in rear l BMW Performance Rotors l UUC StrutBarbarian l Racing Dynamics Rear Strut Bar l Jim Conforti Shark Injector l Light Birch Interior Trim l Bimmian Celly Mount l M3 Trunk Mat l l e90 Performance E-Brake & Shift Knob l M3 Tri-Stitched Boots l AL Headlight Retrofit with ZKW Lenses l CobyWheel Wrap w/M3 Stitching l LCM sw 4.5 triple blink and rear fogs

  10. #10
    Join Date
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    Just a follow-up a few days in...

    By replacing the leaky injector:
    + I haven't had a single warm start issue! Starts every single time, the exact same way.
    + My gas mileage has improved around 1.5 mpg (could I have really been losing that much fuel?!?)
    + Power delivery is smoother (this makes sense, but really did not expect it)

    100% happy guy.

    BMW CCA # 510252

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