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Old 03-01-2011, 01:21 PM
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Join Date: Feb 2008
Posts: 59
1984 380SL Cold Start Problem

Noticed lately my 84 380SL will not start when cold. The motor turns over strongly with a new battery, but the engine will not crank. I hear the fuel pump come on & stop after about 5 seconds (like I think it should). If I come back later (maybe 15 minutes after trying to start it), it will start perfectly. ALSO, for the last few times when it would not start, I removed the air cleaner cover & pushed down/release the round disk in the "throat" & the car started up perfectly. Was this by accident? If not, why would it start when pressing/releasing this disk? What are some other problems? Car idles perfectly once started with excellent acceleration & idles/starts perfectly when hot...just in the morning when cold, it will not start instantly.

I am new to the SL as I have driven MB diesels for 25 years! Any help would be greatly appreciated.

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Old 03-02-2011, 03:30 PM
meltedpanda's Avatar
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Join Date: Mar 2003
Location: Central Ky
Posts: 6,089
a sticky throtle plate will do as you suggest. May just need to be cleaned. When you push it down it should be very easy and then "feather back up" on its own. IF that is OK then your cold start valve may be the issue , or the CSV circuit
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Old 03-03-2011, 12:02 PM
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Join Date: Feb 2008
Posts: 59
Throttle Plate Cleaning

Perhaps a dumb question, but how do you clean the throttle plate? Can I spray a carburetor cleaner in the throat/on plate to clean it?

THANKS for you input!


Last edited by xke190sl; 03-03-2011 at 12:02 PM. Reason: grammar
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Old 03-03-2011, 02:38 PM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
When you press the sensor plate down you are causing the injectors to open. Normally the plate would be pulled down by air being pulled past it by the engine pulling in air. More throttle = more air = more fuel. This is the basic principle of K-Jet.

If you can't feel a binding in the sensor plate when you push it down, then the most likely problem is the warm-up regulator. The WUR lowers what is called control pressure when the engine is cold, making it easier for the plate to move down, providing more fuel when the engine is cold, which it needs to run well. One failure mode for the WUR is that it doesn't lower the control pressure enough for the engine to get sufficient fuel for a cold start and warm-up.

Lots of posts on this.
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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