Running Rough?

Ok guys, well i was driving today and all of a sudden when i slow down my car starts like spuddering. The engine is running really rough. It starts like wobbling forwards and backwards i guess you could say. I put about half a bottle of fuel injection cleaner in a full tank 2 days ago. We just changed the spark plus and wires yesterday. It has kind of a funny smell when idling which leads me to think its the fuel injection cleaner.. But i only added half a bottle to a full tank. We checked all the spark plugs and wires... Its a 1999 Pontiac Grand Am GT. It still runs. It does have 176000 miles on it. Just rebuilt about 7 weeks ago. I was reading that a popular failure for my kind of cars is the LIM gasket from over heating.But the temp. guage stays obo 200.The check engine light just came on.Going to take it to a shop for the diagnostic but was wondering what yall thought it was.Im trying to get into cars and repairing them so would like to know. Thanks!