This is a '91 190E 2.3 with rotary idle air valve. The valve meters air from the rubber plenum below the airflow meter, and discharges it into the port area of the intake runners - i.e. after the throttle valve. This intake port connection uses a Y-shaped rubber hose that connects to the air valve with one branch, and the other goes to plumbing that connects to the valve cover port, the air cleaner, and a small line to the fuel pressure regulator.

I have replaced most of this rubber plumbing, but haven't been able to identify all of it. I fear disconnecting the old rubber for inspection until I can obtain new, since it is likely it will rupture. So, I am uncertain what hidden components may lurk there.

I would think there would have to be a check valve of some sort in this second branch of the 'Y', and wonder why there is any connection at all from these components to the intake port - bypassing the metering circuit?

I have an intermittant high-idle condition, and not understanding what all is done here troubles me. Thanks for any input.

Steve