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Old 08-05-2012, 06:33 PM
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Location: Richmond VA
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1986 420SEL transmission adjustment for idle under load

Leaving aside the issues I have with fuel/air mixture (rough idle), it appears to be worst under load (in Drive), say at a traffic light stop. Idle drops to 500rpm or less, and the engine seems very strained. If I slip the transmission into Neutral, it is much better; idle rpm is then ~650-700.

Is there an adjustment on the transmission to cure this, so the vehicle doesn't feel so strained at idle? Or shouldn't I worry about it?

Simon Shearer

1986 420SEL

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Old 08-05-2012, 08:19 PM
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Location: SE
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With fuel mixture issues I wouldn't mess with the trans. I would correct the mixture issues and I bet the straining would stop.
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Old 08-07-2012, 12:28 AM
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Location: NE Ohio
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I could be wrong but I think idle for these V8's is like 550+/- 50 rpm. There should be a sticker under the hood above one of the headlights saying so.
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Old 08-07-2012, 12:53 AM
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Location: Tennessee
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my 91 420sel idles at 525 in gear and it's smooth. if the economy needle is not pegged to the left then you have a vacuum leak somewhere causing the rough idle. you can also try cleaning the idle air valve to see if it improves the idle

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