Because it only knows a certain range for idle conditions. You need to basically set the base idle value by tuning it in. Then it can adjust for the rest of the range. If the idle value is too high it will lean up to suck less air in, if too low then it will be more rich. Just right and the engine will be happier.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....

I could not really tell him what when or how I am going threw the motions and learning.JNT

Setting is I would say fair,the engine has a very slight roughness at start up, the cold start roughness feels like choking from to much gas, it will last for 3 seconds and runs up to about 900 rpm then settles to 800 then 750 for maybe 10 seconds then settles in at 700,once in gear it falls to 600 to 650. almost completely smooth just a slight roughness all in all I am pretty happy with the performance and the mileage of 19.5 mpg.JNT

check out V12 uber alles site

The engine computer is a very simple one. It's not like the adaptive OBD-II ECU's in more modern cars.

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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.