1999 SR 190 Signature 5.0 Mercruiser - Surging

[Scott Zimmerman]

I have '99 Searay Signature BR
5.0 Mercruiser 240hp fuel injection.

I am having a problem with the boat surging at idle and low rpm operation. It seems to run fine at speed but when you throttle back down it will idle fine and the after about 30 seconds it starts to surge again. Idles about 600 rpms. The problem really starts to show once the engine is warm. Runs about 170 degrees.
Replaced: IAC, Cap & Rotor, fuel pump and fuel filter.

I have seen a couple posts about this being a common problem but cant find the solution.

Anyone have similar problems or a possible solution?

 

[scoflaw]

Monitor your fuel pressure, could be the FPR. TPS is another suspect. A weak coil could have your ECM compensating for it. Weak battery and or charging system

 

[Scott Zimmerman]

Thank you scoflaw