Have you ever replaced the OVP module? Both the modules on my 88's went out within the last year and were still running on the original - they are dated so you should be able to tell. That alone was the cause of the rough startup. I would imagine it could also play some weird games on the idle speed at full operating temp.

One of them also needed a new water temp sensor (located at the back of the head near the firewall on the driver's side, has 2 connectors attached to it) before it would start properly.

__________________
(2) 1988 300 SEL W126