'76 450 SLC - Fast Idle when Cold - Mercedes-Benz Forum

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post #1 of 4 (permalink) Old 07-29-2011, 09:18 PM Thread Starter
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Date registered: Jul 2011
Vehicle: 1976 450 SLC
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'76 450 SLC - Fast Idle when Cold

Greetings, seeking suggestions on my first 450 and still learning it's traits. When cold the engine starts within 5 seconds but runs a fast idle. Once warm, the car is a bit tricky to start and does not run a fast idle. My guess is a vacuum issue but would like to hear the thoughts of others. Thanks!
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post #2 of 4 (permalink) Old 08-04-2011, 06:42 AM
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Cold start valve checked?

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post #3 of 4 (permalink) Old 08-06-2011, 09:44 AM
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Vehicle: 1979 450SL
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I have 79 450SL with the same issue. When cold it starts right up but idles high. After warm it takes 4 or 5 times before it will start. So I'm interested in what you find.
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post #4 of 4 (permalink) Old 08-13-2011, 07:54 AM
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I think both of your cars has the Bosch K-jetronic fuel injection.
The high idle is normal when cold to a point. The warm up regulator (WUR) idles the motor up during warm up to around 1200 to 1400 RPM. As the car warms up the WUR lets the idle go down. Lots of topics on this if you use the search function. Especially in the 107 forum.
The hard start after the engine is warm is typically caused by a bad fuel accumulator and/or check valve on the fuel pump. This is located on the passenger side, US cars, right behind the rear axle. Easy to change but costs around $100.00. AutohauseAZ has them listed at $97.95

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