surging

The EHA is the black Bosch Fuel pressure controller on the CIS. The O rings leak, and so does the unit so spend the coin (number 2 fire hazard in the engine bay) and buy N-E-W!

But before you do all that, be sure all electrical items for IDLE are in proper order: ICV is clean and proper voltage | Grounds are in tact and clean from the starter to the engine bay | wires for ignition are not arcing (check in the dark) and last but not least the COIL.

There are other issues as well, but wiring to and from these components get baked and fragile. These are suggestions of things, your actual results may vary.

To follow on the thoughts here, something is causing a demand or "hunt" for idle. So many things that are electrical, temperature based communication of data to the ECU and the Idle Speed Control Relay. So check the simple things first, electrical connections and vacuum. When checked move to ignition wires to and from cap to engine and coil. Be sure no gas is dripping from the EHA or the Fuel Pressure Regulator. How long has it been since the fuel filter was changed along with accumulator.... (Rhetorical thoughts) Injector seats and cups get hard and brittle too.

just turn car on and remove the electrical from the Idle Control valve. If the idle stays the same (may go up briefly) then reattach it and go to the passenger floor board. Remove the plastic faux floor with a 10mm nut driver, pull the idle speed relay out and replace it with a spare. I suspect its gone bad.

it looks like a black pack of cigarettes, the left module is the alarm and says Becker - you can unplug that in my opinion too. Those are the only two "black Relay" boxes there.