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  #1  
Old 06-15-2019, 11:16 PM
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Overactive AAV idle control w108 4.5

This engine has an Auxiliary Air Valve that is supposed to regulate idle speed, it higher idle when cold and lower when warm. Well, mine seems to be overactive, as the car idles way too fast when cold (1 minute after warmup it will be so high that the ECU will cut fuel, then it falls and gets fuel again, ecu cuts fuel, etc), but too slow when warm.


Is there anything I can do about this?


Thanks in advance.
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1972 280SEL 4.5, silver
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  #2  
Old 06-16-2019, 01:35 PM
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You sure it's not the temp sensor?
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With best regards

Al

Check out the W114, W115 enthusiast website.
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Join the Mercedes W108 group
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  #3  
Old 06-16-2019, 01:53 PM
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The coolant temp sensor for the ECU? When it's bad or disconnected the mixture will be ridiculously rich, so I don't think that's what it is, but I will check it anyways.
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  #4  
Old 06-16-2019, 08:34 PM
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Turn the screw in to let less air through and keep warm idle up using the mixture screw on the ECU. That's what I did. Other than crimping the bulb tighter, that's about all you can do I think.
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Old 06-16-2019, 11:54 PM
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Thanks, I will try that.
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Old 06-17-2019, 07:25 PM
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I should add, you can do the opposite as well, if that works better in your case. Use the knob to lower cold idle and screw on the ECU to raise warm.
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  #7  
Old 07-10-2019, 03:43 PM
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The mechanical bits in this devise get stuck sometimes. Remove the rubber connector pipe and spray in some WD40. Works for me when the idle mechanism gets cranky.
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