2000 330 HP Indmar MPI (injected) engine runs sluggish when throttle is advanced. In fact, if throttle is advanced quickly, it will die. If advanced slowly, it seems to mis or stumble, then "catches" and will run fine. Note, this happens anytime the throttle is advanced, i.e., even if I am going 40 mph and advance the throttle, it stumbles then will catch.

I have replaced the in-line fuel filter and installed new plugs. The analog temp guage reads 175-190 deg.

Any ideas? No dealer near me.