go on Facebook he is on quite of few sites selling his parts,

there many qualified techs out there that can repair your boat, not just one "guru"
what you have there is a simple issue, all you have to do is take to a qualified shop and they will take care of it, I have been in the repair business for a long time, nobody can diagnose your issue correctly over the internet ,its a guess at best, and not every issue requires a ecm overhaul and injectors flushed,,

I would start by having someone that knows what the data readings are and what they indicate and go from there,,if you want to play with it yourself I would stat by checking resistance values on the IAC so you can rule it out.

thanks for that, I am a marine engineer myself, just not a merc gasoline guy. What I did omit to say is that I checked the resistances on the cam sensor and they were out. It’s just been a bit of a mare getting the right cam sensor as there are a few different versions and the version I have is obsolete. I took a gamble on a couple of different ones but neither have been any good.
There is an update kit but everything I order takes a week or 2 to get it in the UK. Not an abundance of 496’s over here either so not many experienced shops.
I will check those IAC resistances too.
more than happy to keep going myself with it, it’s all experience and I’m not looking for one guru, just anyone with helpful information.

all in all I just don’t want to waste 2 weeks waiting for new cam sensor to arrive without checking for other possibilities.

What name does BUP go by on Facebook or other sites?

Google "boats unlimited" for John's contact info

What were the 12V and 5V readings?

Don't know your serial number but if your ready to throw parts at it here is a list

8.1 cam sensors

2001 - Standard PC948, GM 12575182 NLA, Merc 883513 NLA, AC Delco 19338600, Block 1XA, 1XW

2002-2003 - GM 12575183, Standard PC 949, Merc 881666 NLA, Block 2XA, 2XW, 3XA, 3XW

2004+ - GM 12591720, Standard PC260, AC 2133826, Merc 892615002, Block 4XA 0M667238 & up, Block 4XW 0M672041 & up
CDI E13-0004. OEM#: Mercruiser 892615, 892615001, 892615002, Pleasurecraft R020035A
Replaces Part#: Mallory 9-29821 Sierra 18-7646

I know for a fact that John aka BUP works on more 496 s than anyone. They come from all over to get fix. I know from experience and you can go up on FB and ask to see for yourself. here is his website. Call the guy he helps out so many and has fixed stuff that no one else could, www.boatsunlimited.com

thanks for the info

13.1 and 5.00 vdc

I was able to just pick out the part # off old sensor 12575183

serial # M364613

I think 2002 to 2003 engine

If the block code matches then your good