Decel valve...

[Dave Head <dhead@sundial.sundial.net>]

Tonight out of the blue my decel valve began cycling. 
SYMPTOMS:
On a shift the rpm rises (spikes about 300 rpm) - normally an indication
the decel switch is bad. However at an attempt to idle, the engine will
cycle at 1400-1200 rpm (rapidly - every second). Unplugging the WOT plug
results in rpm rising immediately to about 2200 rpm. You can hear the decel
valve merrily cycling away.
CONSIDERATION:
My in the dark (with rain) tweaking tells me that the decel micro is
working since the rpms rise when unplugged, and when lifting the throttle
coming to a stop it does fall initially. Since I know that the ECU detects
the rpm and is supposed to allow the signal to pass to the decel valve at
to open to allow the sensor plate to fall (mit microswitch closed), and
then close it at 1200 rpm to allow the plate to come slowly to a rest, my
idea is that something is preventing the plate to fall. This is the only
thing I can think of. Any CIS gurus out there ever experience something
like this?

Only other possibility I could consider would be some kind of dramatic
change in fuel pressure. It shouldn't be an air leak - it would have to be
massive and the car runs fine off idle.


********************************AUDI FAN***********************************
                                   EMCM(SW) Dave Head  
87 5KCStq 246K miles                1.85 or so... bar 
    qcusa #3442           Oviedo, Florida     plate: STLTHTQ
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