Bad Spark Plugs....The cause?

[NumberOne]

I have a 06 115 Optimax. I have had a rough fast idle since last summer. Every time I start the day its fine but throughout the day it gets worse. Every trip is like this. Its worse if I have to idle a long way. Like a no wake zone or graph an area for a while. Has no problem getting on plain or full throttle. I took it to a mechanic and he said a spark plug was the issue. Went out the next day and it ran great. Never missed a beat. That was last weekend. Took it out yesterday and ran great the first 3 hours than the miss at fast idle came back. What could cause the spark plugs to fail? The mechanic replaced all three spark plugs and it ran great the first time but the second time its starting to miss again.

Also, my bulb seems to not harden when I pump it. It will fill some but doesnt seem to fully fill. This probably plays into it as well.

Actually ran over to get my serial number: 1B481011

Thanks

[JOE54]

over rich running condition , fuel leaking by pulse diaphragm ,regulator diaphrams , injectors ,low air psi,are some...… checked air filter????? often overlooked

[leonreno]

Do you run your motor at idle a lot? As Joe a rich condition could cause problems and they would be exaggerated by long periods at idle. Check your plugs for carbon build up, could post pictures here for opinions.

[NumberOne]

Do you run your motor at idle a lot? As Joe a rich condition could cause problems and they would be exaggerated by long periods at idle. Check your plugs for carbon build up, could post pictures here for opinions.

I dont idle much at all. Especially since the rough idle has occurred.

[NumberOne]

How do I figure out what these spark plugs should be gapped to for this engine?

[leonreno]

Read the faq at the top of the forum, it has spark plugs and gaps in there by serial number.

[SilverFox579]

From the FAQ (see at top of 2.5 and 3L forums) IZFR5J (NGK) @.032-.033 for 75-115 Opti's

[NumberOne]

Perfect. Appreciate it.

[lpugh]

I would question specifically what was wrong with the plugs, Close up Pictures would be useful.

[RetroActv]

I had a very similar carbon buildup problem on a 2004 115 Opti. Plugs would foul up after 5-6 trips, with little to no idling. Could tell by the miss that usually kicked in. Took it in, turned out the coils were bad and replaced under warranty/recall. That was about 10 years ago, have not had a problem since.

[NumberOne]

I had a very similar carbon buildup problem on a 2004 115 Opti. Plugs would foul up after 5-6 trips, with little to no idling. Could tell by the miss that usually kicked in. Took it in, turned out the coils were bad and replaced under warranty/recall. That was about 10 years ago, have not had a problem since.

I think this is my culprit. Gonna have to look at it this week. Didnt those optimax's have a known issue with their coils?

Thanks