190e 2.3 1986 very rough idle

Hi, I'm a newby to this. My 1986 190e 2.3 has been idling very rough for quite a while and I have not been able to find the cause. I suspect the Idle Control Valve
is not working. MB part number is 001411725. How do I test it? Thanks.
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Do a compression test FIRST. Always start with the basics.

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