Search the threads--there are a few recent posts with good details (a 300e, I think.) The basic idea is to remove the air filter, look for the Electro-Hydraulic Actuator (black box, 2 pins, mounted to the firewall-side in my case), hook an ammeter in-line with the circuit, and measure current. I seem to remember it was ~20mA with the key-on-engine-off. In the case of my '89 2.6, it was actually the EHA itself that was worn out, but I needed an OVP in the case of my 2.3. Hope this helps--the other threads explain better, Andrew Seidel.