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.

You sure it's not the temp sensor?

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.

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.

Thanks, I will try that.

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.

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.

Gentlemen,

I open and repair as much as I could my AAV.

Is this normal open position?


And, when reinstalling, should I consider some gasket sealant liquid over the gasket or just the gasket as it is?

No, It should open more, and close when hot. (place in pot ofhot water) There are vids on youtube on cleaning them.

just the gasket.

It closes ok. I already disassemble and clean it. I polished the piston and slider tube ID

I pressed the bulb, maybe too much. I think That’s why it is so much closed.

Would it cause any trouble with just that opening?

We've installed a washer in the rubber hose so that most of the extra air was shut off or sometimes we close it off completely. Engine runs poorly when cold but fine once it warms a bit.

thanks for the info.