hi all to those who have taken the time to read and offer advice, im quite new to the site and over the last few days ive put a few posts on but not getting any good advice( lack of responce).

i have a 2002 1.8 petrol duratec

can anyone tell me if a faulty alternator can cause my car to die when i come to a stop however this can be abit intermitant and sometimes rev as low as 150-200 rpm then recover its self?? happen the other week then some how fixed its self, just been and disconected the battery to clean terminals as my first step to find a battery light on fault. but just niped to shop and yet again the car dies when i come to a stop, can be quite dangerous as you lose your steering etc, i know the first thing you may ask will be the volts readings so here they are using the self dignostics on trip computer:
battery on ignition - 12.6
battery when engine on 13.8, last week when the car was running ok after dying at stops the readings here were at 14 volts, but since today when its starting dying again there reading 13.8.

any help much appreciated
thanks