2002 Saturn SL1 check engine light code P0303

For old models, Saturn/GM also used the same material fiberglass gasket in your model, you almost certainly have a leak from a crumpled, sucked-in gasket as I suffered (and many others). I would say going to Saturn dealership to make repairs is probably not good idea if they are going to put in the same GM intake gasket part. Maybe possible to specify Felpro gasket with whatever shop you go to if you don't do the repair yourself. I would not go too long with your car in that condition as there is localized leaning at your cyl-3, that could cause a burnt exhaust valve there.

The exhaust is extra hot venting out that cylinder. P0303 is misfire at cyl-3. Mine was P0301 (cyl-1). You may get P0507 once in a while when PCM fails to control the fast idle caused by the leak under certain conditions. Most of the time, it is very slow idle caused by 3 cylinders running. You run smoother in cold idle because the IAC opens up to increase idle and end up lowering the manifold vacuum, so the reduced vacuum causes less leaking at the failing intake manifold gasket.

I'd say try cleaning everything with your ignition before replacement; Idle problems could be caused by engine coolant sensor (ECTS). Are you sure it was changed? Did they put on a new wire connector along with it?

Hope helps.

Replace the coil it is most likely bad. observe the engine at night or in a dark environment and proceed to use a spray bottle to lightly coat the coil pack for that cylinder number 3 and if you see an arc at the coil or any where else this will confirm a bad coil but even if you don't see any arcing it still may be a weak coil.