01 s-10 with new motor idles rough

my 01 s-10 i just put new motor in and all of sudden idles rough but can give it gas and it clears up also service engine soon light is on to
any that can help please do

Is it the 2.2 or the 4.3 ? I would take it to Auto Zone or any parts house that will scan for free and have your code(s) read. As this is a new engine, did it come with intake already installed or did you or someone else install it. If it has the plastic intake gaskets on it, it is very easy to over torque and crack them. Thus resulting in an intake leak. Also check to make sure all your vacuum hoses are properly connected.