1997 Yamaha 225 SWS Rough Idle

[P2870]

My STBD engine recently began to idle poorly and shake more than the Port I have checked and or changed the following...
Compression test ( ALL WITHIN 10 PSI 110-120), Primary and secondary fuel filter, new primer bulb, 3 new LPFPs, new spark plugs ( all 6 spark checked ok pulling each wire one by one), cleaned VST (was not dirty), all 6 injectors checked out like new as per tech and report, cleaned O2 sensor( wasn't too dirty), shift microswitch appears to be working correctly (noy shorted out) , Is the black stain a symptom of rich or lean fuel mixture? I ordered a new NTK O2 sensor to try. Looking for the test harness for O2 sensor as well.Part Number?
Any other suggestions?

 

[rejesterd]

Based on what you've done, I would not think it's related to fuel delivery. However replacing the spark plugs only rules out bad plugs. You could still have an issue with spark due to a bad coil or plug wire. Get a spark tester tool (at any auto parts store) and test each plug wire. That will confirm good spark in all cylinders. If you see good spark, then check for air leaks around the intake manifold with brake cleaner or starting fluid.

I would think the service manual will tell you the part number for the O2 sensor test harness. If it's carbon-fouled, that means then engine is running rich, and it will continue to run rich because the fouled O2 sensor will tell the computer to go even richer. But it got fouled for another reason.

 

[P2870]

Thanks I pulled each sp wire ine by one and can hear spark jumping gap I will get a spark checker to be sure. and try my new O2 sensor. Hopefully that makes it right.