...carefully read this whole thread. Also go to the link posted by melek4me on page two of this thread (complete with pictures and shop manual pages). If that isn't enough information, you might have to take it to a shop.
XJC: I finally got around to digging into the diagnosis per your info.
Vacuum from the solenoid end to the plugged line ends is solid-no leakdown whatsoever (so much for the cheap fix idea!) My left IWE has a very slow leak. I can actually hear the actuator move when I release the vacuum to the actuator though, that's kind of cool. It works as it should until it leaks down. I can fix that. The right side... Even with the vacuum hooked directly to the right IWE it won't disengage. That concerns me a little as the leak rate is similar to the left side. I guess I know what I'll be doing this next week after I gather the parts.