87 325is idle problem

["Delaney" <ddelaney@xxxxxxx>]

I have been suddenly stricken with a terribly fluctuating idle on my 87
325is (89k).  The RPM cycles from about 1000 to about 2000 RPM, with a
period of
about 1.3 seconds.  Rich running condition is obvious as the smell of fuel
is high and the car hesitates upon acceleration, and plugs are wet after 
idling.  The idle
 does not change substantially as the car warms up.  The Motronic system 
spit out a 3 flash
fault code (only once in five days), which my Bentley manual said was faulty
temperature sensor, but it tested fine and replacement showed no change
(also disconnecting it does not stop the cycling).

I have tested most of the sensor inputs at the computer harness and all
check out OK, including the idle air valve resistance at rest.  I have not
checked fuel pressure as I do not have the equipment.  I can find no vacuum
faults.  Air and fuel filter, plugs, cap & rotor, and the above mentioned
temperature sensor are new.  The idle valve looked fine when I had it off
and the piston was free and seemed fine.  This condition started very
suddenly so undue engine wear or catastrophic failures seem unlikely.  Any 
help with
this problem would be appreciated.  Please reply directly to
ddelaney@domain.elided

------------------------------