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Thread: I'm sure someone here knows the answer... (94 E320)

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    Member northNH's Avatar
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    I'm sure someone here knows the answer... (94 E320)

    My recently acquired '94 TE would start easily, hot or cold, but immediately upon starting would briefly hit ~1500RPM before quickly settling to a normal smooth ~600RPM idle. No other running issues, excellent grunt...

    Last week I pulled the (correct) plugs, which were well-worn, with gaps measuring ~0.050-0.060" [1.27-1.52 mm]. New plugs at 0.035" [0.09mm], issue resolved.

    Electronically, precisely if possible, what exactly did the car do to get itself started that resulted in the brief high idle?
    Could this happen like this with a CIS-E car?
    '92 300CE Black/burgundy Sportlined
    '94 320TE Silver/gray
    '86 BMW 635CSi Black/black 5spd
    '67 Volvo Amazon wagon Green/green 75Kmi time capsule
    '62 Volvo Amazon Black/red 4Dr 65Kmi time capsule

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    Re: I'm sure someone here knows the answer...

    You sure its 1500? M104 cars (at least in the W202 I owned) keeps the idle high and the shifts long from the ECU on cold starts to warm up the cats to meet emissions standards. It usually isn't 1500, more like 1200.
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    Re: I'm sure someone here knows the answer...

    This ain't that, since correctly gapped plugs has eliminated the momentary start-up high idle spike...
    Now max idle RPM on start-up, hot or cold, is ~1K, like my CIS-E car has always been.

    i was going to swap the worn plugs into my CIS-E car to see if I get the same high idle spike, but it's too damn hot, and wondering aloud here seems easier, and hopefully more enlightening.
    '92 300CE Black/burgundy Sportlined
    '94 320TE Silver/gray
    '86 BMW 635CSi Black/black 5spd
    '67 Volvo Amazon wagon Green/green 75Kmi time capsule
    '62 Volvo Amazon Black/red 4Dr 65Kmi time capsule

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    Re: I'm sure someone here knows the answer...

    Quote Originally Posted by Harv View Post
    You sure its 1500? M104 cars (at least in the W202 I owned) keeps the idle high and the shifts long from the ECU on cold starts to warm up the cats to meet emissions standards. It usually isn't 1500, more like 1200.


    My HFM Mercedes of the era do this on the first "cold" start of the day. For example here is a video I just took of my 1997 M104 S280's first startup of today:



    My thoughts have always been that this is because the engine is in Open loop mode on the first cold startup. That is that the ECU could be waiting on the coolant temperature to reach a certain point, Oxygen sensor to warm up (and provide varying output voltage) or that a specific amount of time pre-programmed in has elapsed perhaps as a catalyst warm up strategy. I havent delved into WIS to check this out but I did not find a need to as I do not think this is an error.

    And the cold gearbox upshifts will be delayed also in order to warm up the catalyst or O2 sensor faster (I do not particularly like this feature as I prefer to keep throttle input and RPM to minimum levels with a cold motor)

    Note that the 500E board recommendation for spark plug gaps is 1.0mm which is what I run on all my cars and appears to work very well.
    Last edited by JC220; 07-03-2018 at 03:51 PM.
    1987 w124 200 - 3.6 AMG build | 1990 w124 300E-24 | 1992 w124 500E

    1994 320CE Sportline | 1997 w140 S280 | 2007 w211 E220CDI

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    Re: I'm sure someone here knows the answer...

    +1 on the 1.0 mm plug gap. That was my first thought when reading NoNH’s thread but JC covered it.
    Last edited by TerryA; 07-04-2018 at 08:33 AM.
    Terry

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    Re: I'm sure someone here knows the answer...

    Now I am confused.
    Are you saying the reason the idle does not now shoot up to 12-1500RPM (as it should?) is because the plugs are gapped to 0.9mm rather than 1.0?.
    The gap will be heading towards 1.0 on it's own, will pay attention to this as it does...

    As an aside, is there a surgical strike that will eliminate the cold gearbox upshift delay?
    '92 300CE Black/burgundy Sportlined
    '94 320TE Silver/gray
    '86 BMW 635CSi Black/black 5spd
    '67 Volvo Amazon wagon Green/green 75Kmi time capsule
    '62 Volvo Amazon Black/red 4Dr 65Kmi time capsule

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    Re: I'm sure someone here knows the answer... (94 E320)

    I think most on this board (I would guess probably 80% of us) will agree that the 1.0 mm plug gap helps the performance overall from the get-go. It will idle better as well and stop the stumbling misses and will help as well with acceleration and fuel mileage.

    As far as waiting for the plugs to spread out to 1.0 mm on their own. They will probably be worn out by then. 15K miles is about all the plug life you have.

    Just my $0.02
    Terry

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    Re: I'm sure someone here knows the answer...

    Quote Originally Posted by northNH View Post
    As an aside, is there a surgical strike that will eliminate the cold gearbox upshift delay?
    Yep. Pretty sure you can disconnect (and plug both ends) of the small solenoid next to the brake booster that has a vacuum line running to it from the right (passenger) side of the transmission.


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    Re: I'm sure someone here knows the answer...

    Quote Originally Posted by a777fan View Post
    Yep. Pretty sure you can disconnect (and plug both ends) of the small solenoid next to the brake booster that has a vacuum line running to it from the right (passenger) side of the transmission.
    Correct. Don't forget to also pull the bulb for the CEL on the dash too.


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    Re: I'm sure someone here knows the answer...

    Quote Originally Posted by a777fan View Post
    Yep. Pretty sure you can disconnect (and plug both ends) of the small solenoid next to the brake booster that has a vacuum line running to it from the right (passenger) side of the transmission.
    Done. (Only plugged the solenoid line to the trans, still electrically connected).
    Success on this 40° AM.
    I like it.
    Thanks

    Quote Originally Posted by gsxr View Post
    Correct. Don't forget to also pull the bulb for the CEL on the dash too.
    CEL has not noticed the change.
    Yet?
    '92 300CE Black/burgundy Sportlined
    '94 320TE Silver/gray
    '86 BMW 635CSi Black/black 5spd
    '67 Volvo Amazon wagon Green/green 75Kmi time capsule
    '62 Volvo Amazon Black/red 4Dr 65Kmi time capsule

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    Re: I'm sure someone here knows the answer... (94 E320)

    Excellent. Yep, re-reading my description, I see that its a bit poor in the way I discuss plugging the lines. I meant to indicate that you want to cap off the now open end of the solenoid, otherwise a vac leak will occur when the valve is energized. You can also cap the vac line that runs to the transmission, but other than having a path for debris to get in there, I don’t think there is any harm in leaving it open.


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    Re: I'm sure someone here knows the answer... (94 E320)

    I did exactly as you described in your first post which was plenty clear to me, and I did plug the vacuum line to the trans as well, to avoid any more debris in my life.
    '92 300CE Black/burgundy Sportlined
    '94 320TE Silver/gray
    '86 BMW 635CSi Black/black 5spd
    '67 Volvo Amazon wagon Green/green 75Kmi time capsule
    '62 Volvo Amazon Black/red 4Dr 65Kmi time capsule

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    Re: I'm sure someone here knows the answer...

    Quote Originally Posted by northNH View Post
    CEL has not noticed the change.
    Yet?
    Most likely, yes... it will take a number of cold starts before the DM notices and complains. If not, that would be a bonus!


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    Re: I'm sure someone here knows the answer...

    Quote Originally Posted by gsxr View Post
    Most likely, yes... it will take a number of cold starts before the DM notices and complains. If not, that would be a bonus!
    You are entirely correct, O prescient one...
    5th start after modification triggered the CEL; reconnected lines, cleared light, now back as before.

    I have since discovered that with a cold engine with transmission vacuum line connected normally, momentarily shifting back to N and back to D once RPMs rise above ~1500 for the first time will prevent/cancel the "cold" motor reaching it's intended ~2800RPM before ultimately shifting up to 4th.

    For now seems ideal; I do wonder if this behavior will persist or change as winter approaches and a cold motor is actually cold.
    '92 300CE Black/burgundy Sportlined
    '94 320TE Silver/gray
    '86 BMW 635CSi Black/black 5spd
    '67 Volvo Amazon wagon Green/green 75Kmi time capsule
    '62 Volvo Amazon Black/red 4Dr 65Kmi time capsule

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    Re: I'm sure someone here knows the answer... (94 E320)

    Just curious, is your wagon(?) of the era with the bad wiring harness? If so, has it been replaced?

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    Re: I'm sure someone here knows the answer... (94 E320)

    Yes it is and yes it has...
    Whatcha' thinkin'?

    Snow's been gone now 4-5 weeks...😉
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    '92 300CE Black/burgundy Sportlined
    '94 320TE Silver/gray
    '86 BMW 635CSi Black/black 5spd
    '67 Volvo Amazon wagon Green/green 75Kmi time capsule
    '62 Volvo Amazon Black/red 4Dr 65Kmi time capsule

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    Re: I'm sure someone here knows the answer... (94 E320)

    I was thinking about a 400e I have that had the old harness and experienced the same symptoms as yours. Once I replaced both harnesses the symptoms went away. So the upper has been replaced on your car, has the lower harness been replaced?
    Last edited by MB V8; 08-30-2018 at 05:34 AM. Reason: Wording

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    Re: I'm sure someone here knows the answer... (94 E320)

    Quote Originally Posted by northNH View Post
    Yes it is and yes it has...
    Whatcha' thinkin'?

    Snow's been gone now 4-5 weeks...
    Admiring your fleet and farm.

    How old is the ‘homestead’?


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    Re: I'm sure someone here knows the answer... (94 E320)

    Quote Originally Posted by MB V8 View Post
    ...and experienced the same symptoms as yours. Once I replaced both harnesses the symptoms went away. So the upper has been replaced on your car, has the lower harness been replaced?
    No symptoms now that vacuum line reconnected; I believe it is now working as intended, briefly holding rpms up before upshifting when cold...
    Only upper I believe.

    How old is the ‘homestead’?

    1802...


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