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Idle problems

   My car ('87 5000CS TQ) is having idle problems. The car normally idles
   at 800 RPM but lately, the revs have begun to drop to 400 or 600 and
   the car sometimes stalls. This is especially the case when the A/C is
   on and the clutch is depressed (its a manual) when the car approaches an
   intersection. The revs drop low suddenly and the idle stabilization system

Check for air leaks in the input tract. My '83 TQC had this problem - would
run fine usually, but would intermittently "stall" with no warning. Turned
out to be a [very] slight tear in the flimsy [and effing expensive] air
hose between the air metering box and the turbo inlet. Depending on the
phase of the moon, the tear would open or not and completely screw the
idle air mixture (let in air downstream of the air metering flap), stalling
the engine. Ran fine off idle (air leak was insignificant at higher volumes
at speed). A trick I used [learned] on my Lotus is to run a slight stream of
water around/over suspect joints/etc. If there is an air leak, you will
usually be able to hear a change in the engine cacophony (slurping sounds
of water being sucked into a hole where there shouldn't be a hole is sur-
prisingly "obvious" despite all the engine noise), and the engine usually
reacts adversely to a sudden replacement of air volume with water volume
going into the cylinders . . . Be careful of water on hot spots where it
just sizzles off . . .