no idle when freezing

[S. Jaworski]

88 5000s quattro
Had car all prepped for long trip. Took off early at 3 AM. Very cold - 12
deg F. Tooling along on Rt 80 for 30 miles at 70mph. Came to toll, slowed
down . stopped . .car stalled. Turned on ignition, car started, but wont
idle. Engine runs ok if RPM's kept about 1200. Turned around to go back home
. . had to use engine braking and handbrake for stopping. Car ran fine on
highway. Same problem with idle all the way home on side streets.
Never had these symptoms before.
Later this morning, started car . . idles fine. Took car on same hwy . .same
mileage . . tested idle every few minutes . . no problem. Temperature was
now 25 instead of 12.
Previous symptoms - temp gauge reads low all the time - during trip the
gauge was just off the peg - but I get heat in the car. The gauge will
register higher 25 - 35% in city driving. I have the new thermostat, but
didnt have a chance to install it yet.
I suspect a sticky idle control valve when it was very cold - - congealed
gunk buildup inside.
Anyone have an opinion?
I've read here to use brake cleaner fluid to clean the valve. Is using
Gunk's Air Intake Cleaner any better/safer?

syljay at optonline.net

88 5000s Quattro
90 100s Quattro
85 4000s - - just sold . . still crying over it

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