S-Class (W126) 1979-1991: 300 SE, 300 SEL, 380 SE, 380 SEL, 420 SEL, 500 SEL, 560 SEL, 360 SEC, 500 SEC, 580 SEC, 300 SD TURBODIESEL, 300 SDL TURBO, 350 SD TURBO, 350 SDL TURBO

86 420sec running rough

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Old Dec 9, 2009 | 09:47 PM
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'86 Benz W126 420 Sec
86 420sec running rough

Hi Guys

420sec 175k Miles run on premium unleaded (98-95ron)

Latetly she has been running a little rough, as it gets warm the oil pressure needle bounces between 0 and 1, it has a shake at idle like its abit low (sits at 600-700rpm).

Yesterday while i was coming home from buying oil/filter/oil flush for her, she died while cruising in top gear at about 1500-2000rpm twice and wouldnt restart straight away, had to give it a couple of minutes.

any ideals?

cheers

Nik
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Old Dec 12, 2009 | 07:13 PM
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380se
How does it idle when first started up from cold?

How about warm when you restart?
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Old Dec 13, 2009 | 09:46 PM
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'86 Benz W126 420 Sec
idles pretty good when cold, as it warms up it gets rougher and lately struggling to restart straight away once warm.
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Old Dec 19, 2009 | 07:43 PM
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The control loop on these guys is fairly dependent on all the pieces doing their job.

When cold, they run open loop. After they warm up then the computer controls the mixture. There is a way to open up the temperature sensor and then the computer will think it is cold. I did this while checking my car out, I thought the sensor was on the passenger side of the car down by the oil filter and it was as simple as pulling the connector on it.
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