I finally decided to tackle this SAI issue today. Took about an hour
It was the changeover valve. I popped the top off and found about 3/4lb of rust keeping the valve shut.
I cleaned it up with some CLR and a wire brush. It's working fine now, but I will order a replacement because the rust will come back. At least it's easy to get to.
Before cleaning:
I now have a p0134 for an O2 sensor...probably related to my clutch job (those connectors were a b*tch and something probably isn't seated properly).