I found this on another site
If the Twin spark engine is NOT idling OK (at about 900 rpm), but
suddenly go to about 1500rpm then down to about 500rpm then jump
between these values a couple of times then back to 900rpm.
The engine might even stall during this.
In most cases, there is an easy 10-minutes cure:
With a screwdriwer you loosen the spanner ring around the airintake-tube
at the point where it connects to the throttle-house.
Pull and bend the black intake-rubbertube a bit to the side and spray some
WD-40 onto the butterfly-valve. Let it work a minute or two, and then wipe
the inside of the throttle-house and the butterfly-valve with a clean cloth.
Oh - yes, you have to use one hand/finger doing the cleaning, and your
other hand/fingers pushing the top of the valve, so it opens and allows
you to clean up the inside. Would be nice with a third hand, though.
The reason for the erattic idle is, that over time the butterfly-valve picks
up dirt in the air-intake-tube. The dirt prevents the valve from completely
closing. The engine therefore gets confused thinking the valve is a bit
open (- thinks, that it is you putting your right foot to the pedal
You might have to reposition the idle engine to fix this completely after doing
the above. The way to do that is:
1. Insert key and turn to last position before start. Let it there for 90 seconds.
2. Then turn back off for 90 seconds (with key in).
3. Then start up the engine not using the throttle for a few seconds.
If this is not the cure, you can have a faulty idle speed motor and then
it has to be replaced.
Big thanks to Per here at the alfa156.net Forum for most of this info!
Posty have made this pdf guide including pictures of how to clean it
for the V6 engine. Thanks a lot, dude!
Warning: I have received info from one reader who actually broke his
throttle body trying this. So BE CAREFUL doing this!
Read the unlucky experience from one user in the forum.