Help, my G20 acting funny when starting!

[Erik Erik]

Most of the time in the morning when its freshly starting my 1992 G20
hesitates to start, you hear it cranking and igniting but it wont hold
its idle unless I add gas for a few seconds, other than that it will try
to die out. I just change the oil to 10-40 and its still giving the same
problem, but just about daily when you least expect. Even when I drive
all day long and let it sit for about an hour, here we go again....  The
problem just started, as soon as I change to 5-30 oil two months ago

I got my last tune up exactly two years ago, new wires and plugs(bosch),
and everything else in-between. Is it time for a new tune up already?
Please Help.