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#1
08-06-2009, 09:59 AM
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oscillating Idle 1967 250se
Here's a question- my 1967 250se coupe has an oscillating idle.
when I first turn the key, the engine starts up, revs and then shuts down. next try, the engine revs up, not quite as high, then does not quite stall, and then oscillates up and down, until it warms up. once warm, it still oscillates a bit, but not as much. all this without touching the accelerator pedal. any idea what causes this? maybe some sort of thermally controlled cold-start valve? maybe something is sticking? It's a bit odd!
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 ------------1967 250SeC 1979 450sel 6.9 (usa) 2009 S550 
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#2
08-06-2009, 10:03 AM
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Check the CSV test port for by-pass leakage ..common problem on MFI's......and be sure the Oil level is correct in the Injection pump reservoir...my bet is it is over-full from fuel contamination.
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A Dalton Last edited by Arthur Dalton; 08-06-2009 at 11:17 AM.
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#4
08-06-2009, 11:58 AM
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Quote:
Yes..could be... but one wants to check those two common problems first..you can not adjust the MFI A/F mixture adjustments until you have determined if the richness is coming from a leaking CSV or an over-full reservoir. And then you also have to have spec. timing before pump adjustings....... On the cold running problems , the suspect is a stuck/dirty WRD . Easy fix. Check CSV and Res. level first and someone here will run you thru the other possibles.
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A Dalton Last edited by Arthur Dalton; 08-06-2009 at 12:05 PM.
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#5
08-06-2009, 12:15 PM
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I agree with Mr.Dalton, check what he suggests first.
I might add, that a proper valve adjustment and a 100% igntion system should be verified before work on the mfi system is started. I mean that in a general sense, because sooner or later the mixture is going to be adjusted, and the valve adjustment and ignition system being spot on will help the old girl run at her best. These old-timers can soldier on without attention to these details, but they really shine when they are "tweaked" just right.
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"I was a dirty bird, Carol's not grungey - she's *****in" John Milner....American Graffiti
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#6
08-06-2009, 12:25 PM
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Very good advice ..I have been doing MFI tweaking for many years , and I wont even touch the adjustments until I have done spot on Ign., valve adjust, head retorque, and fuel flow/pressure test.. Only then do I do linkages and a/f mix adjustments. But when I get done, you are tweaked and you know it.
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A Dalton
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#7
08-06-2009, 10:41 PM
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there must be a vacuum leak. Check the venturi valve at the intake snout , as well as the bypass hose that come soff of it. This icertainyl a vacuum leak/high idle setting issue.
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Pierre Hedary 1985 280SEL, 1970 111.026 in progress Mercedes technical advice hotline: 407 765 2867 [servicing older Mercedes in the state of Florida with competence and passion]. From the standpoint of an honest MB technician, Vegetable oil is a threat to your diesel engine's mechanical integrity.
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#9
08-07-2009, 01:13 AM
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An oscillating idle is caused by a vacuum leak. Check all hose clamps and make sure they are tight.
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Regards Warren Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL ENTER > = (HP RPN) Not part of the in-crowd since 1952.
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#10
08-07-2009, 12:48 PM
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Quote:
Touche on the head retoque before the valve adjustment.  Many moons ago, when my dad passed his M116 powered W109 down to me, I asked him when the last valve adjustment had been done. He gave me a blank look, and then got really irritated that the MB "specialists" that had looked after it for ten years had never suggested it.
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"I was a dirty bird, Carol's not grungey - she's *****in" John Milner....American Graffiti
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