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#1
05-29-2008, 02:37 PM
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450SL cold engine surging
Hi--
My 1974 450SL "surges" when cold. It starts right up, idles at normal cold fast idle for about 5 seconds, then starts quickly alternating low to high idle speed until it gets up to about 170 degrees, at which time it drops off to normal low idle. I've pulled the air slide control valve and checked it by heating and cooling it-- it seems to be working properly. Any ideas out there? Thanks. 
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#2
05-30-2008, 02:08 PM
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There's a post on the Benzworld 107 forum that has additional links on this issue. Offhand, I would say that you are getting a LOT of extra air through the aux air valve, and the brain is cutting the fuel at 1500 rpm causing the fluctuation. So you need to check for air and (maybe) vacuum leaks.
__________________
Chuck Taylor Falls Church VA '66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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#3
05-30-2008, 02:16 PM
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Need a timing light for this: Check the ignition timing advance at the front crank pulley.
The mark O should stay steady at around 10 BTDC and not be wandering back and forth. The hunting you describe is often due to weak distributor bob weights. There should be no mechanical advance below 1200RPM. Check the vacuum capsule for leaking.
__________________
[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ] "A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."
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