ok....finally figured that status light out. Never had a code in that area, so I hadn't known about the 'off' light in the CCP being used as a diagnostic tool. I did that particular test and the Off light stayed lit. Tried manuvering the ISC plunger and determined the new ISC is defective, in that it was hanging....once bottomed, it wouldn't return properly. Brought it back and have another for replacement.....Wells brand. Had I known the brand beforehand I'd not have purchased it, but maybe this one will be good. I'll deal with it tomorrow and let you know how this works out. Thank you for the good help, I appreciate it very much.

Upon further review: I have the new unit, but decided to take the OEM unit apart. Cleaned the corrosion from the electrical parts and NOW I'm asking what grease should I use? Choices I own: white lithum/blue HT wheel-bearing/black chassis/regular dark yellow wheel-bearing/vasoline. The '87 grease was hard and caked. Electrically the old unit checks out fine.

All better now. Installed new unit and it's performing correctly. Old OEM unit would not test good everytime. It would occasionally, then it wouldn't, so I trashed it.

My ISC is causing problems very similar to yours.
 

My ISC is causing problems very similar to yours. I had rapid thumping. idled to high and not coming down. In the error codes it also says the E26 error code. How much is a ISC? Where do they sell them?.... and is it hard to install with out a professional mechanic to help out?
Talk to you soon,
Jason Micallef