Engine issues

A few issues with my OB, hoping someone can offer advice.

2005 15 HP Johnson 4 stroke.

Occasionally I get a low oil pressure warning, the red light illuminates on the front of the engine, it idles down and runs rough. Shut down the engine, restart and it runs fine. The oil level is full so I'm assuming it's a bad sensor. Would you agree with that assessment and do you know where the sensor is located?

Second issue. It often, but not always, idles rough and will stall unless throttle is increased, at high speed it's fine. Sometimes it idles very quietly and smooth. Has new spark plugs and fresh gas. Screen in the fuel filter looks clear. It can also be difficult to start but again, not always.

Thanks guys

Seeker, I'm not a pro mechanic, but lets see how close I get to what you find is wrong in the end. I think your oil sensor is failing , as you thought. Don't know where it is. The run rough symptom is trash in the carb or injection system. Sea foam is a great product used since the 40's. Just follow the directions. If that's not it then I think you may be dealing with some ethanol damage problems. It damages the rubber parts and other things throughout the fuel system. Were it mine I would take it to a REPUTABLE pro. Just cuz they're close don't make em good. You may have to drive some to get to one. Again, I'm not a pro. Just read all I can and pay attention when smart people talk. Blue sta bil helps a lot with the ethanol damage prevention. Please keep us posted on what solves your problem.

Thanks it may be an E10 issue but I'm not sure yet. I bought it used and haven't used it much. This was perhaps the fourth time, unfortunately it was during a week long fishing trip to upstate NY. I was able to run and fish but as I said terrible slow idle and stalling unless I throttled up....PIA coming into the dock. Since I've had it I've run fresh gas with E10 treatment, the guy before me I don't know, though my impression is that it mostly sat, of course it may have "mostly sat" full of bad E10. I checked the fuel filter, replaced the primer bulb and fuel line, new plugs, new water pump. I Sea Foam deep Creeped it earlier today, didn't solve it. So off to the OMC/Bomb guy tomorrow, very reputable mechanic who I've used in the past.

Surely a 2005 motor was built to tolerate E10?

I just had someone tell me that he thinks it could be the coil packs are bad.....beats me. Probably take to the mechanic tomorrow though I hate to think what that will cost.

The spark should jump 3/4" to 1" the tool i use is(Great Neck/Adjustable ignition spark tester (25069) | Ignition Tester | AutoZone.com
it is cheap and i use mine all time .on the 2 stroke outboad I fined if it dont jump 3/4to 1 .the coil pack is weak. hope this helps

If the idle is set too low it would cause those problems. Idle should be set with the motor in the water and in gear. Also try running some Sea Foam thru it.

Clogged jets in carb, now running fine.