Cleaning an ERG valve

For my 1990 300SE (gas) Mercedes, it's been suggested I clean my EGR valve to help with the NO2 levels (it's failing emissions). I was told to use a coat
hanger.
The valve works okay, in that the plunger operates easily. But what about "cleaning"? There appear to be only two holes: One in the side of the valve's metal block at the base, and one in the center of the rubber 'cup' inside the valve where it meets the mainfold. I'm hesitant to just cram a coat hanger in eitehr hole, as I don't want (for instance) poke a hole in some rubber mechanism.
Can someone desribe (in text) how this is done? For example, should the plunger be withdrawn when I'm cledaning the hole?, that kind of thing. Or is there some graphic resource on the Web? Thanks.
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Before you try to clean the valve which probably os ok.... test it 1st. Have the engine at idle. Disconnect the hose from the valve. Apply vacuum to the valve with a hand pump if you have access to one. If not, you can get manifold vacuum from the nipple on top of #6 intake runner. With vacuum opening the egr valve, your idle should be very rough. If yes: you have a tired catalytic convertor. If no: 9 out of 10 times, the tube is plugged between the valve and intake.

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