Volvo Penta 5.7 l GiF, recently purchased, history uncertain. Engine starts OK, but idles a little roughly. If i advance the throttle, it gets very choppy from about 700-1000 RPM, then smooths out. Even when warm, the idle is not smooth and it stumbles at 700-1000 RPM. I've change the fuel filter twice, new plugs, StarTron fuel additive, cleaned spark arrestor. Next I will try some fuel injector cleaner. Also, I'm not certain if the low pressure fuel pump is too noisy or not. It does whine some continously. Plugs were not a nice tan color; more of a dark brown. It seems to run normally outside of the problem range and will reach 4600 RPM at max throttle (low end of max RPM range).
Would appreciate any advice.
Would appreciate any advice.