1997 GMC Jimmy runs rough

at start up the engine will sometimes turn a few times before starting and run rough. it shakes at a stop, once on the freeway it runs good.
I have been told the following
engine light does come on when it gets warmed up

i was told that my iec valve may need to replaced

also someone told me my timing belt could be going out

can you please give me the correct steps to take

thank you sirs
greg5