This is from a February 2001 article by Steve Brotherton, an MB tech at Continental Imports from ImportCar online magazine.

“The EHA is the final servo device for applying the corrections intended by the control system. All forms of enrichment are accomplished by increasing the differential pressure within the fuel distributor. The EHA acts as a controlled leak depending on current. Positive current flows cause enrichened mixtures by leaking down the lower chamber pressure (higher differential pressure). Negative current flows cause lean mixtures and, on deceleration, a negative 60ma causes fuel shut-off.�

As you can see if the valve is sticking, damaged,leaking, or otherwise not working correctly, the adjustments needed for the engine to run smoothly are not taking place which may result in a rough or high idle, hard starting, stalling, and poor acceleration.

Look under the air filter housing attached to the back of the fuel distributor. It has a plug going to it and is bolted on by 2 bolts. Mine were hex bolts, but may also be flat head bolts. Google w201 eha valve and look at the images so you know what it looks like.

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1990 190E 3.0L