ur-quattro 20v: bad isv???

[Dave.Eaton]

i'd appreciate some assistance with a problem that i'm having on the
ur-quattro...

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the idle speed is all over the place, from peaks of around 2k, down to
normal - seemingly regardless of load or situation.  it is an intermittent
problem.  a classic case of a malfunctioning isv ???

well....

1) no codes are logged.

2) measuring the resistance across the isv show a higher resistance than
normal (9.5 ohm, where normal is 7.5 to 8.5 ohm).

3) however, removing the isv and using the control element diagnosis tests
to check it shows that it is operating normally from stop to stop, although
with a little scoring obvious on the rotary valve, but there is no sign of
any hesitation of movement.

so....

observation of the basic motronic settings shows an interesting value in
display section 1.

where the idle speed is too high, the value in section 1 (engine
temperature) is in the 80's, which is way too low.  section 1 values should
be from 184 to 215 which correspond to 80-105 degrees c.  so, as far as the
motronic is concerned, it thinks that the engine temperature is -20c!
mmmmmm....

with the engine temperature value as described, section 3 values (current
engine speed) range from 106 to 125.  way too high in other words.  section
3 normal is 77-83 which corresponds to an engine speed of 770-830 rpm i.e.
it should not be greater than 83.

basically no other display section values are out of range (actually the
ignition angle is too high, and the lambda control too high, but i think
that these are the consequence of too high an idle speed).

so, it leads me to think that the actual problem is not the isv, but the
engine temperature sender or possibly the thermostat.  however, there is no
way, in summer in new zealand (ambient outside temperature over 20c), that a
bad thermostat will result in an engine temperature of below freezing - so
it's not likely to be the thermostat...

therefore its the temperature sensor.

to test the sender, i need to remove the it and check the resistance (it
should be 1-5-3.0 kohm).  which i've yet to do...

questions:

1) does a bad temperature sender sound plausible?
2) do i have to remove the inlet pipe to get to the sensor in the rr/3b
motor (inlet pipe is above the manifold in the rr motor).
3) any experience or advice from listers?

thanks for the help,
dave
'95 rs2
'90 ur-q