[urq] engine coolant temp sensor q (long)

[n-engelbert at terrans.net]

Car in question is 83 UrQ with WX engine.

I've measured the sensor near cyl 1 and seen no change in resistance to
ground as it stays at 1560 ohms or thereabouts when cold, warm, hot, etc.
I thought I remembered reading somewhere that this is the ECU coolant temp
sensor, is this the case, or is it a temp gauge sensor?  Its part number is
035 919 501.  It's a one pin sensor.

Or is it the sensor at the back of the head that is the ECU sensor?  Part
number, 056 919 369 P.

The reason that I'm asking is that I'll be trying to track down my warmup
issues this weekend and along with replacing vacuum lines, testing fuel
pressures, and testing duty cycle, I assume that the sensor at the front of
the head should be replaced as it isn't working correctly.  My mech tells
me fuel pressure is correct though the fuel pressure is bleeding off
quickly after shutdown.  He suspects fuel pump check valve, but the pump is
a new pierburg off a 90 with internal check valve.  I could try to plumb in
an inline check valve if that would help.

I recently replaced the injectors, inserts, orings, and O2 sensor while
replacing an exhaust stud that backed out.  What is the possibility the new
ones are leaking, which may explain warm start problems and would explain
easy starts when the car is very cold in the mornings, residual fuel in the
cylinders?  My mechanic says he set the mixture when he last had the car,
but that hasn't helped the problems.  I could test for leaky injectors as
well.

When I first noticed the problem, when the car had been sitting overnight
and it was below about 55 degrees F outside, the car would start but idle
very poorly and stumble upon acceleration until the turbo built boost.
This would happen until the car had a chance to warm, and it seemed as if a
switch was thrown because the car would all of a sudden settle into a nice
idle and have great throttle response.  If I were to open the hood when the
car is in the stumbling state, I can hear the airflow plate slamming open
and shut when I pull the throttle body open to rev the engine.

Now, when it's particularly cold out, the car will start and run strong for
a couple of minutes, and then get bad for 10-15 minutes, and then smooth
out.

I'd really like to get this sorted out this week during the holiday when
I've got a garage to work in.

Suggestions, BTDT, etc. is greatly appreciated.

Nathan Engelbert