Do you have any engine codes? If so please post. Fouled and failing catalytic converter, low fuel pressure due to fuel pump or fuel filter issues. Broken or dirty MAF sensor. Old spark plugs and wires causing incomplete combustion and a rich almost flooding condition. Failing ignition control module. The list goes on. If you don't have any codes (yet) have catalytic inspected and clean your MAF sensor and see if that helps. If it doesn't you may need to take to a shop for a diagnosis.