1972 280SEL 4.5 W108 high idling - Mercedes-Benz Forum

 
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post #1 of 10 (permalink) Old 07-26-2013, 02:11 PM Thread Starter
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Vehicle: 2006 C230 Sprots V6, 1972 280 SEL 4.5
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1972 280SEL 4.5 W108 high idling

Any suggestions on why my W108 would be idling really high and if there is a manual adjustment I can do to lower the idle. Throttle position seems to be set properly. Could a poorly functioning mass air be a contributing factor?
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post #2 of 10 (permalink) Old 07-27-2013, 06:30 AM
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Is this a recent issue? Or has it always been high? The adjustment is a big screw-like knob with a spring on the front of the engine.
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post #3 of 10 (permalink) Old 07-27-2013, 03:43 PM
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Most likely the air regulator is stuck it will require removal and descaling or replacement. This is right next to idling screw .
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post #4 of 10 (permalink) Old 07-28-2013, 09:59 AM Thread Starter
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Is this a recent issue? Or has it always been high? The adjustment is a big screw-like knob with a spring on the front of the engine.
I recently purchased her and she was in such poor condition. I don't know her history. I cleaned out the map sensor which was clogged and it made a small decrease. The oil pressure now actually drops to thirty when at a stop. However, on idle it still remains high. I will check the adjustment today. Thanks for the advice.
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post #5 of 10 (permalink) Old 07-28-2013, 10:02 AM Thread Starter
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Most likely the air regulator is stuck it will require removal and descaling or replacement. This is right next to idling screw .
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I do notice that the throttle body is sucking in air very strong. Do you happen to have a photo of the air regulator? Thank you for your help.
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post #6 of 10 (permalink) Old 07-28-2013, 06:41 PM Thread Starter
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Okay, I managed to find the air regulator and noticed that the adjustment valve was pegged all the way down. I will need to remove and repair or replace the vale. I also played around with the MAP sensor, fuel regulator, and air filter sensor. I bypassed the air filter sensor for now as it is faulty (I get 0.18 ohms on my meter). It was sending a signal to increase the idle. So far the idle is perfect and the engine has new life. I took it out for a test drive and brought it up to 120mph. Such a nice feeling
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post #7 of 10 (permalink) Old 07-28-2013, 11:03 PM
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thanks for updating Good diagnostics.
Air regulator can be cleaned and made operational if it sticks and causes high idle
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post #8 of 10 (permalink) Old 07-28-2013, 11:06 PM Thread Starter
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thanks for updating Good diagnostics.
Air regulator can be cleaned and made operational if it sticks and causes high idle
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I bypassed the air regulator for now. I was looking online for a replacement but will take your advice on cleaning. Thanks for your help.
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post #9 of 10 (permalink) Old 07-29-2013, 07:07 AM
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I've done the same thing - removed the air temp sensor wire. In my case, the engine runs poorly with the sensor hooked up, meaning the aux air valve is performing poorly (unlikely, as it's less than 6 yrs old), or I have air leaks in the intake somewhere. In any case, I'm getting about 13 mpg on the highway, which isn't stellar, but is close to the 17 the car is rated for.

I'd recommend you NOT fiddle with the MAP sensor. There's nothing to fix on it, and the adjustment screw requires a gas analyzer to set the thing properly.
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post #10 of 10 (permalink) Old 08-16-2013, 06:11 PM Thread Starter
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I recently replaced the aux air valve with a used air valve from another 280SEL 4.5. The idling problem is still there but I now can control idle via the idle control adjustment. It still idles high which leads me to believe that the used aux air valve isn't 100% percent functional. I am considering replacing the the valve with that used by a W116 450 which shares the same M117 engine. The main difference is the height of the valve. The W116's aux air valve is slightly shorter and is still available brand new from Mercedes. The W108's is no longer available from MB. I was under the impression that Mercedes guarantees replacement parts for 100 years.....
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