fuel fluctuation at 2000 RPM and lower

[sdamato]

I have a 1999 370 Aft Cabin with twin 7.4 Horizon Merc 380 HP engines and I started having a problem where my engines will surge by themselves when running under 2000 RPM's. It is almost like a low fuel pressure where my idle will be going up and down by itself. Once I go over 2000 RPM's I do not have the problem. I have replaced the MAP (Manifold Absolute Pressure) sensor but that didn't fix the problem.

Has anyone else had this problem and what did you do to correct it.

 

[Larry]

These motors are notorious to "hunt" (unstable RPM not under load) under about 1800, there is no known permanent fix, although if you replace the spark plugs it seems to get better for a little while, I f this is the same symptom that you are experiencing.

 

[sdamato]

Thanks larry, I do have new spark plugs, cap, rota etc...The boat was fine all last year. There has to be something to replace that will fix it. My mechanic is trying to trace the problem but so far coming up blank.