Ide check that the sparkplug wires are all the way in , check the spark plug wires, and all the ignition systems, ie distributor cap, and so on. I had my explorer sport trac oil changed and when i picked it up it the check engine like was flashing and i had loss of power . After i pulled back in the shop and told them i noticed that the #1 spartpug wire was loose and hanging out, so the #1 pistion was not fireing that why the loss of power. the whole engine and truck was shaking, as soon as we put it back everything was ok. I thing the guy who did the oil somehow pulled the wire out checking and chaging the oil. So check all the ignition systems.