hope people dont mind me posting this as is not on a fiat....is my old volvo 440 1.7 turbo my baby

just a weird prob my alternator has developed. if i let it idle the car shudders after about 5 mins and the battery goes flat

so assuming battery not being charged by alternator easy. however...if i start the car and give it abit of a rev for a second the alternator kicks in and its charging at a health 14.5 volts.

im thinkin of replacing alternator anyway , it was only fitted about 3 years ago but i reallise these parts dont tend to be new just refurbs