'86 4kq--intermittently rough when warm

[Mike Veglia]

This one is for all you CIS-E experts out there. First off a bit of history
(and an admission I haven't yet done everything possible that I know I
should still do). My '86 4kq was running rough and down on power for a brief
period during warmup for a  while. One day I took a look at the connector to
the CIS coolant temperature sensor and noticed the connector was looking
rather ugly. Upon reconnection the car wouldn't start--so I knew (thought?)
I was on the right track. Cleaned up the connector and it seemed to get
better, but would still intermittently run rough--now more often when fully
warmed up rather than during warm up. Aside from an oil change, gas, and
go...I haven't yet done much to/for this car since we got it last Spring.

Saturday I went through and replaced vacuum lines, cleaned electrical
connectors and grounds, etc. I still need to change cap/rotor/plugs, and
suspect I maybe should change out the CIS coolant sensor as well. When I
took the car out for a drive afterwards it seemed to run much better--for a
while. Then it got to a point when fully warmed up that it gagged off idle
and puffed black smoke, obviously way too rich. Got home and didn't have
much more time to deal with it, but I did put a duty cycle meter on the test
points and read ~36-38 at idle and ~44 or so with some throttle applied. I
recall on Huw's page the idle duty cycle should be closer to 27? Is this a
clue?

In addition to the obvious I know need to change anyway (plugs, cap/rotor,
and temp sensor)--of which only the temp sensor is likely to have any
effect, what else should I check for? The o2 sensor age is unknown. Car has
~145k miles on it. There do not seem to be any more potential vacuum leaks,
the upshift light works, and when the car is running right it has
appropriate power (this is my 4th 4kq plus I've had a CGT) and pulls strong
all the way up to the rev limiter. I'm at somewhat of a loss as to how to
properly troubleshoot this, since I really have had very few CIS troubles to
have to troubleshoot over the years. Thoughts? TIA!

Mike Veglia
Motor Sport Visions Photography
http://www.motorsportvisions.com