Just had my water pump and intake manifold changed and a whopping cost of 1,200. on 2003 Chevrolet Venture

Now my car is vibrating and acting like its going to die when I stop at red lights or drive thrus and the mechanic says its nothing they did. What could be wrong?

Asked by for the 2003 Chevrolet Venture
Was it running that way before the work was done, sounds pretty fishy to me.