rough idle

I am new to this . my first time.

i just bought a 1995 blazer le
my problem is this
the truck runs good but today the check engine light came on and i noticed that it idles a bit rough when in gear and in park.
this started when the check engine light came on.
other than that it drives normal.
has anyone out there run across this problem and if so ,what can be done to fix it.