Lupo 1.4 16V 75 hp.

Good morning:

a few days ago the Lupo (1.4 75cv) was pumping to change the filters and spark plugs, but continued to fail according to the manual had to change the alternator belt (Poly-V). I change it but still does not solve, it is closed when starting it when it is slowed down, after a while it is shown less, but when the thermoin turns down the thermaline shit. I appreciate the comments or possible site to bring it to be economical. Thank you