89 100, difficult starting, poor running

[David Conner <conner@cfm.ohio-state.edu>]

Well, I'm about to give up and take this car to the shop for help.
This will be my first defeat since I began subscribing to this list over a
year ago.
Unless, that is, someone can point me in the right direction.
I'm afraid it's a long shot, but here goes.
The car is an 89 100, non turbo, engine code NF, 2.3 liter w/ CIS III E all
electronic injection.  
I'm looking at a Bentley for the earlier models, 84-88, but I think the
basics are mostly the same. 

The car began running poorly about a week ago, missing, poor starting,
stalling at idle, etc.  

The problem was intermittent at first and sometimes the car seemed to run OK.
Now it has gotten worse to the point where yesterday it would, scarcely
start or run at all, bothe with the engine warm and cold.

I changed the cap rotor, and plugs, checked all around for leaking hoses,
corroded wires, etc and found nothing.  Fuel and air filters were changed
recently.

Today, the car starts and runs but idled poorly when cold, better when warm,
and the engine stumbled on acceleration. 

The engine fault display, when the ignition is turned on, keeps signaling w/
the symbol for engine coolant...either too hot or too low.  Neither of which
is the case.  
The coolant light comes on even w/ the engine cold, and the coolant is full.
I should mention the coolant temperature gauge hasn't worked for years and
is disconnected.
The Oxy sensor is original and the car has 80k miles on it.

Bentley says the engine has the ability to display fault codes, activated w
a fuse inserted into the fuel pump relay etc. but I can't get it to do this,
maybe because the coolant warning light won't go away?  Or maybe the
diagnostic electronics are screwed up?  

So, as I said at first, I'm about to give up.  
If there's anything real obvious to anyone, please give me a shout.
TIA,
Dave Conner, Columbus OH   e-mail:  conner@cfm.ohio-state.edu   
'87 5000S     '89 100