VP 57 will not idle 2006 5.7

"2006 Volvo Penta 5.7 Gxi-FF

After a short run (15 mins) at about 3800 RPM, the engine died when decelerating to idle speed. Would not start again until I throttled up a bit while cranking the engine. We hobbled back to the marina and the troubleshooting started.
It was time for a tune-up anyway, so replaced the cap, rotor, wires, plugs, belt, pcv valve fuel filter…along with an oil & filter change. Although it ran better once it was started, it still needed additional throttle to start – and has a hard time keeping idle. There are no issues at higher RPM – anything above idle purrs like a kitten.

I did some research and decided to change the IAC valve. This didn’t change the initial symptom – but it gave me some additional info.

If I manually compress the IAC valve, the engine starts right up – idles high but regulates down to 600 RPM after the IAC makes it’s adjustment. Turning off the engine, seems to ‘reset’ everything and I’m back to square one (i.e. hard to start / will not start). If I remove the PCV valve and let more air flow freely into the intake (without the PCV in line) it starts, idles and runs without any obvious issues. So – my conclusion at this point is to replace the MAP/MAT sensor….. seems to me the air flow/pressure is not being sensed correctly and the ECM may be sending incorrect signals to the IAC (and possibly other components) causing a rough idle.

Am I on the right track? Anything I’m missing? Does anyone have other suggestions or alternate checks I should try before replacing more parts?"

"May want to get a scan tool a

"May want to get a scan tool and check the other sensor inputs (engine [coolant] temp for one) to make sure they aren't providing bad (but legal) values.

Based on your decription, the IAC portion is normal and the "leaning" procedure with the PCV indicates a Rich condition that gets offset.

A coolant temp sender being "cold" will drive a richer mixture. Make for hard starts when warm, etc.

I don't think the MAP would do it as there isn't a big difference between the pressure at idle (normal) and with the PCV line open."

"May want to get a scan tool a

"May want to get a scan tool and check the other sensor inputs (engine [coolant] temp for one) to make sure they aren't providing bad (but legal) values.

Based on your decription, the IAC portion is normal and the "leaning" procedure with the PCV indicates a "Rich" condition that gets offset. (In other words the air flow is fine; the fuel provided is incorrect for the air flow.)

A coolant temp sender being "cold" will drive a richer mixture. Make for hard starts when warm, etc.

I don't think the MAP would do it as there isn't a big difference between the pressure at idle (normal) and with the PCV line open."

Hello,
i realize this is a few years later, but did you ever figure out what the problem was?
I am experiencing the exact same issue with my 2006 VP 5.7 GXi.
Went through the same things, plugs, wires, cap, filter, IAC motor, map sensor...to no avail.
After replacing IAC, boat ran great. Did a 45 mile day trip and ran great until we got back to our marina and I brought it down to idle and she stalled out on me. Was able to get it restarted after 5 attempts, and idled roughly over to dock.
I'm wondering if it is The ECM.
Any help would be appreciated.