1999 225 efi

by Craig
(Port Huron, MI, USA)

I have replaced:
Bad coil pack
crank position sensor
Ignition and Fuel packs
Grounds to everything
Cable from the battery
Water separator from the tank and the one on the engine.

rebuilt the VST
Cleaned the fuel rail and Injectors.
cleaned the screen on the fuel regulator

Each fix has made incremental changes and now that it seems to be idling and running really good at low RPM's, when I advance the throttle half way the engine begins surging from dead to running about every half second. Backing off the throttle smooths it out. I can get it up to nearly 2000 RPM's before it happens.

Does anyone have an idea what this can be

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