Mercury 40hp EFI sputtering at low rpm

[xXTJTHEBOATER95Xx]

Hi everyone,

I have an issue with my 2002 40 hp Mercury 4 stroke EFI serial number:OT523239

Basically, when I start the engine from being cold, it runs fine and I can go out for a ride, idles fine and runs good at a decent cruising speed of about 2200rpms on my 13 foot Whaler then about 15 or 20 minutes later when I go to throttle down, the engine starts sputtering and isn't happy. It wants to die at the most inopportune time like when I'm about to dock or just slow under 2200 rpms. I can see the fluctuation of about 100 rpm on the tach. When I give it throttle, it may get back up to over 2200 and run fine or it will bog down really hard. And a few times I've heard a popping sound like detonation maybe.

Can anyone help me figure out where to start?

Also if it does die, it starts back up every time without an issue, but still will have sputtering issue.

Thanks,
​​​​​​​TJ

 

[damorgan]

What do the spark plugs look like? Not 100% sure but could be something with the plugs. I wouldn't suspect a sensor issue if it only does this when at operating temp, but I wouldn't rule it out either. I would think maybe a fuel issue, but again, you should see poor running at all rpms if that were the case I would think. Just my $0.02, i'm not an expert with the engine by any means, but do own/maintain this same type/model