Sporadic rough running in neutral and idle

Merccoper

Petty Officer 2nd Class
Joined
Jun 23, 2018
Messages
108
Asking for my brother on this one.

It’s a 2009 60 hp mercury EFI. As the subject line says, it runs rough (not so much as a cough/sputtering, but more of shake/knock…like not running smoothly). It does this sporadically, hot or cold. More often when it first starts it has this symptom and then will suddenly stop, purr like normal. But let it run long enough it will start again. Same thing happens when at trolling speed.

Runs totally smooth as you give it gas.

New spark plugs.

Any thought?
Thanks!!
 

Dave1027

Lieutenant Junior Grade
Joined
May 25, 2010
Messages
1,080
If I was to guess, I'd check, fuel filters, fuel pressure and do a spark gap test. Being an intermittent issue, it may be hard to nail down.
 
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