I have the same problem - I have my Alfa 156 cutting out and I am able to start it after 15 mins.
I have read all the treads and I have l have found the RPM Sensor (or should I say felt) at the back of the block behind the starter but I have a big problem I can't get the bolt out ! I have the cuts, burns and bruises to show for it. The bolt holdling the sensor in place (Is it a 5mm Hex head ? or a star head ? or square ?) "The bolt head seems after lots of trying to be angle upwards ? Is that right ? Am I using the wrong tool, I now its not a standard bolt but are they the star type head or the Hex's or square allen keys ? - I have thought about going underneath and trying that but I cant see you have a better chance because of the lack of space and if the bolts angled up then I think it would be impossible. "I have taken the trottle housing off which wasn' to difficult but I still cannot get in far enough, the hoses near the gearbox always seem in the way as does various wireing. I have had a look at takeing the black plastic intakes off at the back of the engine but I cant figure out the rigid pipe at the passenger side it looks fixed lower down to the block Is this an engine out Job ?
I would be very greatfull of any help ! I have being trying this job on off for three days and I still cant get the thing done. I have also tried the wireing to the MAF that seems ok I have clean the earths up on the passenger side and also checked the reset button for the fuel cut off under the seat.
Any recomendations for the right tools and the best way to tackle this.
Big Fan of Motori Italiani - Have ownded 33 Quadrafoglia Verde, 33 Giadinetta,147 x 2, 156 X 2, 156 Sportwagen x1, Lancia Prisma x 1, Fiat Uno x 1