EE Question -- Some Kind of Circuit Interference with AC Clutch Spark Table Switching
 

I recently made a software mod to fix my 1st gen MSPNP AC idle once and for all:

https://www.miataturbo.net/megasquir...de-hack-73751/

While I was working on implementing this, I discovered that the MSPNP was not doing spark table switching as expected. When I first installed the MSPNP, I implemented spark table switching and verified operation. At a later date, I also implemented the purge valve solenoid mod. These two circuits looked like this (1J to AC Clutch, 2X to Purge Valve Solenoid):

https://www.miataturbo.net/attachmen...1&d=1373386531

Long story short, when I removed the purge valve solenoid circuit from 1J, spark table switching began working again. This is OK because with the code hack I don't need the purge valve anymore, but it bothers me that I don't know why there was interference. It looks like it should have worked OK. ??

why do you need spark table switching for a/c?

It's for AC idle where I run more timing in the idle region. One of the recommended methods from the sticky. My code hack also uses the signal to increase the IACV DC.