Ok thank you for the reply'That's the throttle plate stop screw. On the Motronic S4 cars you do not ever touch that.
There isn't any way to directly set the AFR on the Motronic cars. What problem are you trying to fix? If your mixture is way off it's typically a bad oxygen sensor, temperature sensor, or an air leak. On the S4 if your "check engine" light isn't coming on then the mixture is almost certainly fine.
If I need to set idle how would I be able to?there was a little blanking cover over that screw from the factory.....maybe someone has been turning it before?
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remember these tachs can be inaccurate with time.........check your 'actual' idle with an external instrument (some digital multimeters have a tach readout)
RPM is around 800 to 900. The engine is a little rough on idle and after running around town . The IAV is new so no hunting.View attachment 1703237
If all the sensors are working as they should, giving correct signals back to the ECU, and if there is no false air, the idle should be spot on.
what is your idle at the moment? is it at least smooth or is it hunting?
you could remove and clean the IAV, that's an easy job to do. (there is one allen head securing bolt on the clamp, remove that, remove the IAV and squirt some brake cleaner spray into it....give it a shake then allow to dry and replace it........use a blob of silicone grease on the rubber seal that it fits into on the plenum...that is a common air leak spot when this fat soft seal hardens and shrinks a bit.
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new plugs in and new big air hose.I'd check for any small air leaks.
check for leaks around every air hose connection using carb cleaner or brake cleaner spray.
next I would remove the big air hose and the hard plastic hose from the plenum and reach in there with a soft rag soaked in brake cleaner fluid and clean the throttle butterfly flap and that whole area.
what plugs are you running, are they burning clean?....maybe just put in a new set of NGK B7ES and see if things improve .......they are cheap enough, and changing the plugs you need anyway to remove the big air hose (time to thoroughly check it for small splits, and clean that butterfly)