After I cleaned ours (1991 190E 2.3), I noted its movement was free all the way to the stop, where it remained open a slight amount. I was satisfied it was stopped mechanically at this point, and the opening was still sufficient that any slight wear would not have made any difference.
I tested it with a bench power supply, so I could adjust the voltage/current supplied it, and it appeared to react smoothly, consistently, to the applied voltage on its terminals. Testing prior to cleaning revealed a certain gumminess to its action, and repeatability was not so good. Since this device is inside loop control for the idle speed, I suspect the engine controls can recover from most ills of this device other than jamming, failed electromagnet, or air leakage.