CIS IIIe diagnostics etc

[David.Payne at brinksinc.com]

I'm trying to read the codes on a 1989 90q.  The build date is 04/89.
According to the Bentley CD the '89 models (49 state) don't have a Check
Engine bulb installed and you use a diagnostic plug under the dash instead
of fuse in the fuel pump relay.  I can verify that the check engine bulb is
either missing or burned out, but I can not find the plug that Bentley says
is there.  Can anyone give me a closer location other than drivers side
under dash?
I'm trying to trouble shoot a couple of ongoing problems with this car.
Things that I know or have done:  New (last 10k miles) injectors and
mounting hardware, all new ISV plumbing, new CIS boot, thoroughly cleaned
ISV (this week), newish (last 20k miles) cap, rotor, plugs, wire, temp
multiswitch.  While the car is warm and running I get 13v on pin 2 going to
the ISV (this is a two pin ISV) which makes me think that will open the
ISV.  Plugging the ISV in or out makes no difference, leaving the ISV
plugged in or out makes very little if any difference in the way the car
drives.  Triggering the WOT switch makes no difference in volts going to
pin 2, unplugging the 2 pin temp switch (on a warm engine) makes no
difference in idle or volts on pin 2.  Can someone explain the ISV circuit
logic to me?  The Bentley CD is a little vague.
To compound the problem I have a vacuum leak that shows up once the engine
is hot.  It sounds like it is coming from the intake manifold right were
the ISV hose goes in.  Squeezing the hose feeding the ISV closed makes the
leak go away and almost kills the engine at idle.  If I crack the throttle
slightly, I can hold revs and get the leak to go away by squeezing the
hose.  Soaking the area with brake cleaner will eventually get the revs to
go up.  I want to have a better idea of what's going on before I pop off
the top of the manifold because then I won't be able to run the engine.
Anyone had problems like this before?
Last problem (that I'll talk about today) is an intermittent lean condition
at WOT.  It gets lean enough to get a good hesitation, but most of the time
it pulls strong.  I don't know if the lean out is related to the ISV issues
or not.  I would think that since the ISV air supply is downstream of the
air flow sensor that even if it was wide open all of the time the fuel
would be compensated.
Sorry for the long post but I'd really like to put some of these issues to
bed.  I love this car when it's acting right and have invested enough in
Bilstein's, H&R's, etc. to try to get some enjoyment out of it, and besides
it's cheaper than $350 a month for a Imprezza or Mazda 6 wagon (just a few
of what I'm currently Jonesing for).
Thanks, Dave.