my car will start but as soon as i touch the gas petal it dies,fuel pump was changed 14 months ago

i tried it a few hours ago it will idle but as soon as you try giving it a little more gas it dies,i tryed it a little while ago and now it idle for
like 10 secound and then dies.engine light comes on every once in a while
i checked it with a gm code key and it gave me a code 42,also the altinator changes high all the time,any ideas?