on/off reading of 90.5% or actually 90% means:
Electrohydraulic actuator current is implausible. A 90% duty with a running engine means the same thing. You are supposed to get 70% as it is a Fed car. Check the current with engine off/ignition on; you should see -20 mA. If you don't see that, check your OVP relay behind the battery.
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer