It's not a "valve" - just EHA or electrohydraulic actuator. It fine tunes the fuel flow to maintain stoichiometric mixture for emission control under control of the ECU based primarily on input from the O2 sensor.

If the EHA is disconnected fuel metering is determined by the mechanical metering capability so it effectively becomes a mechanical FI system like the prior K-Jetronic system. If the engine operates okay with the EHA disconnected, there is probably something wrong in the "E" part of the system, which includes the ECU, 02 sensor, other engine sensors, and the EHA itself.

You cannot "scan" a '87 model engine because they are not like modern OBDII engines, but they do have some limited diagnostics.

You should run the duty cycle test, test EHA current, and O2 sensor output. You also need someone - either yourself or a professional mechanic - who understands the KE system and what tests to run to isolate faults.

Lacking this you could possibly get into an endless parts changing loop, which can be very expensive and not solve the problem.

One problem that is common on older cars is connectors. Electronic system operate on small voltage differences and currents, and a bit of corrosion at connectors can cause intermittent problems. In some cases, systematically inspecting and cleaning all connectors can eliminate intermittent faults.

Duke