I posted a similar question with my 1896 420 SEL. In my case the vacuum line to the EZL was disconnected when I bought the car. I did not find out about it until I checked the timing and realized that I was at 5 degrees instead of 12. When I re-connected the vacuum to the EZL the rpm went up as well as the timing (it went up to 25 degrees). The idle is as high as yours. I had a mechanic check it - looked for leaks but none were found. Cleaned the idle valve but it did not help.
My next step is to follow the diagnostic on the CD: Measure the current through the idle valve and check for proper operation of the throttle contact switches.
Please keep us posted on how your investigation progresses.