My wipers have been doing the same (145). They were fine on continuous sweep, but struggled on intermittent, but intermittently
The problem : too much grease in the wiper motor preventing contact fmro the trailing pins to the circular track. When I mean too much grease, I mean more than enough to keep a CV joint happy for eternal life!!!
Take off the arms, then the plastic covers, then unbolt the linkage and remove the wiper motor. Under the black plastic cover is the motor - at the back a white plastic clip on cover (where the contacts are), remove this and be amazed! Use lots of kitchen roll and remove all the grease. Then apply a very thin layer of a thick grease on the circular track, put back together and enjoy intermittent sweep wiping.
Just done this today, took all of 1 hr. Funny thing is, this happened this time last year, the car was still under warranty. I waited 4 weeks with cr4ppy wipers for it to be looked at, then verified it needed a new wiper motor, then another 6 weeks to get one in & fitted. So for the cost of £300 odd quid the claim was for, Alfa could have saved themselves some money/time had they looked into what the real problem was..
@Ian R : I wish I'd been there when that happened, im in stitches just reading about it!!! It reminded me of the time my Fiat decided to play silly buggers with the horn. Sat in slow moving traffic on the M40, horn going on, off, on, staying on, on permanently. The best bit was - it stayed on even when the fuse was pulled out
so I had a great journey back home through town with constant horn on!