92 S-10 CPI V6, running rich on passenger side

A buddy has a 92 s-10 with the CPI V6. It has started missing at idle and at cruising speeds. The check engine light was on, so we had that checked and it turned out to be a bad EGR valve. We replaced the valve and that turned the light off. It still misses though. It will smooth out under hard acceleration. I pulled the plugs, and the passeneger side looks very rich, but the driver side looks normal. I have heard this could be the "spider" in the manifold and that these are expensive. Could some one help me with this, and also explain the purpose and workings of the spider?

This will tell you all you need to know. Not a tough repair except for the fuel lines at the rear of the intake. Good explanation here: http://forums.s-series.org/viewtopic.php?t=2278