75 TwinSpark bad idling

[Lars Arvidsson <arvid@xxxxxxx>]

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

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