Questions for engine techs

[buckbuck]

My 2008 212X (462 hours) port engine is not running smooth at idle. Placing the YDS on it and watching the sensors I noticed the following irregularities compared to the starboard engine;

*-Ignition Timing Before Top Dead Center normally ran at 5 degrees. Occasionally would go to around 16 degrees.

*-Throttle Position Sensor was bouncing around. Normally about 0.742 volts but sometimes would drop to 0.698 volts.

*-Throttle Valve Opening normally ran at 1.1 degrees. Occasionally would drop to -0.3 degrees. The spreadsheet cell this number was in would turn red at the same time.

*-Just to note that the Fuel Injection Duration fluctuated around 3.0 milliseconds. This was consistent with the starboard engine.

What do you guys think? TPS giving bad info to the ECM which in turn drives the timing to a default setting?

Is the timing degrees displayed from an output of the ECM or an input from a crankshaft sensor?

How is the Throttle Valve Opening derived? From the TPS?

Note that I had the oil analyzed and there is very little fuel in the oil. I changed the injectors last year when I suspected they were the problem.

 

[Murf'n'surf]

I thought that the TPS would throw a check engine code when it faults?

I think you might be on the right track with the TPS.

 

[itsdgm]

Have you changed the spark plugs recently? Most engine related issues on our vintage boats are spark plug related. Hope you figure it out soon.

 

[Speedling]

Very good chance it is the TPS and it would make sense logically that way.
I would start with that for sure. I don't know what costs are, but you can do the parts swap tryout first.

 

[buckbuck]

I have changed the plugs twice since this problem has started. Also replaced fuel injectors and ECM. With the oil analysis I am confident I don't have the dreaded stuck fuel injector problem. It runs fine above idle. It just occasionally runs rough and I can't leave it that way. My troubleshooting leads me to the TPS or perhaps the Manifold Pressure Sensor. Both require removing the entire air cleaner assembly.