FW: 75 TwinSpark bad idling

[David Masters <david@xxxxxxxxxxxxxxxx>]

Lars asks ...

Hello out there!
I'd be most grateful if someone could give me a clue on this one.
My dear lady in red, a 75 twinspark 1990 has developed an illness.
The idle tracking is bad, mostly I get 1000-1200 rpm, warm as cold.
It fluctuates sligtly, and it doesn't seem to response to load
variations, like the
headlight on/off. The rpm just decreases a little.
On some occations, I suddenly just get no idle at all, the engine stalls
instead of idling.
The engine does not sound as nice as it use to, sounds a little rough
and nerous on idle. No pinging, as far as I can tell.
When driving, it works just great, good power and smooth handling. Just
a little doubtful after throttle has beeen in idle-position.
Sofar I've tried:  Checked all cables, groundings, and relays. The
connector by the four relays. Check O2-sensor, reading
is correct, fluctuating symmetrically around 0.45 V. Engine termo sensor
is OK,  fuel pressure regulator replaced.
No vacuum leaks can be found. No loss of motoroil.
A clue, please...

best wishes Lars in Sweden
1990 Alfa 75 TS
E-mail: arvid@domain.elided

[]  Cleaning the idle stabiliser (on the side of the intake plenum) and the 
air flow meter may help.  I had a similar problem that has gone away since 
the clean up.  Also wash out the vapour separator with petrol or kero.  Use 
some injector cleaner in the tank with your last fill-up before an oil 
change.

Alfisto@domain.elided asks what a crank sensor is.
Surprised as I was that one had failed.  What it does is track the position 
of the crank using a toothed pulley on the front of the crank. It is an 
inductive pickup, and rather sensitive to its proximity to the pulley. 
There is a double tooth missing to let it know where TDC is.

YMMV,
Cheers,
david
1989 ALFA75 TS
Newcastle, AUSTRALIA.

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