Toyota Repair: 1994 Prizm 7-1 CEL - Cant seem to get at the source, chevy prizm, bright flashlight

Question
1994 Chevy Prizm
1.8 liter / Manual trans
California emissions package (key here)

It's been throwing the 7-1 CEL code for about 3 months. Engine runs fine. The repair manual says it's the EGR valve "system," which on the Cali car is more complex than the 49-state version.

Manual says 4 things can cause this:
1. EGR Valve
2. EGR Temp Sensor
3. EGR Vacuum Switch
4. ECU

I have replaced all of these except the ECU (which I suspect they just throw in as catch-all under most of the codes).

Still throwing the same CEL.  Other than electrical tape over the CEL, any pro-tips? Is there a way to test the ECU? It's gonna need to pass emissions probably later in this year.

Thank you very much for any hints you can give me on what to check next.  

Answer
Did you clear out the ECM after you
installed these components?
Don't condemn the ECU.

I'm not familiar with the California
cars but many times Its usually something
inexpensive and simple.I've seen where
this issue is caused by a bad vacuum
hose or connection. Spend a lot of time patiently
inspecting all hoses for cracks or disconnect and
all wire connections. Use a good bright flashlight
if necessary.

Tim