Another o2 sensor?

[Rich Z]

I’ve experience an o2 sensor going bad or clogged on higher rpm. Is it possible for the same symptoms to show on idle to about 1500 rpm? I’m having an issue with idle and while accelerating. Went through everything on this motor and I’m back to the o2 sensor. All plugs look little lean especially #1. Motor is rough on idle. It stumbles and feels like it lost a cylinder or two till about 1500rpm but runs fine after that up to 6k

[JUST-IN-TIME]

what motor?

[21XDC]

Sounds like a tps adjustment may be needed.

[Rich Z]

It's a ‘02 225 ox66. Tps checked good .49-.51v. Also swapped ecu and different tps. Installed new thermostats thermo sensor and thermo switch. One thermo switch tested bad. A while back I adjusted my shift linkage because my prop was making a clicking noise. Since then it was hard to shift in and out of gear. Shop manual describes a shift interrupt switch may be bad if lower unit is hard to shift. Inspected the shift rail and when in neutral the linkage was off center by .5”. The shit rail pivots and the shift interrupt switch may have been engaging when in gear causing two cylinders to cut out. Shift interrupt is only supposed to engage while shifting, cutting two cylinders out for ease of shifting in and out of gear. When this switch is bad it will cause a rough idle by intermittently cutting out two cylinders. Ran good on a hose. Will test boat tomorrow on lake and update. O2 sensor is still a suspect. It’s only showing 5.3 ohm instead of 100ohm on heat element wires.

[Rich Z]

Shift interrupt switch was the problem. Adjusted my shift linkage so that the shift roller sits in the center of shift rail in neutral. No more rough idle or surging on low rpm. It took me almost a month but I finally got it. Guys, if your prop is making a clinking noise in neutral make small adjustment on shift linkage or you will have the same problem as I did. Make more significant adjustments by dropping the gear case and adjust the shift rod accordingly.