These vehicles are very reponsive to the choice of spark plug brands and gap styles. The manufacturer's recommended plug is a Denso # 3132 (KJ16CRL11). This plug may not be as easy to find as some other brands; but it is well worth it to use. It is available online from Rock Auto (www.rockauto.com). The plug gap should be .040" (1.0 mm).
I would also recommend thoroughly cleaning the fuel injection throttle body.
These two things can work wonders with this very sensitive motor.
If you can find a gas station that sells gas with no ethanol in it; that would further improve the running. There is a nationwide list of ethanol free gas stations at www.pure-gas.org