2002 Mercury 200 SX DFI serges at idle

[Costa Plente]

I have noticed this the last few times that I took it out. While sitting out of gear at idle the RPM will increase then decrease and return to normal a few times. It has started doing this more just recently but it runs fine otherwise. Has anyone else had this problem and how serious is it. The serial # for the motor is OT430660.​

[EuropeanAM]

How wide is the RPM variance (ie: Rpm's range 565 - 635 RPM's).

[Costa Plente]

Sometimes it's alot less than others but from what I could tell it was usually between 500-600.

[EuropeanAM]

Normal operation is a PCM controlled idle speed of 565 (+/- 50) RPM's. In other words, if the engine idle speed remains between 515 - 615, that's considered relatively NORMAL.

[Costa Plente]

Maybe I didn't explain it correctly. The motor will be running at normal idle then without me touching the hotfoot the RPM increases and decreases on its own and it continues to do this until I put it in gear. The amount of RPM increase is between 500 to 600 RMP. Once its in gear everything seems to be ok and has no problems.

[EuropeanAM]

Gotcha. So now we're talking about an idle ranging from 565 RPM's to 1100 or so RPM's. If so, I agree that it's not normal and needs to be addressed.

Have there been any changes (electrically) involving a trim sender, Fuel or Oil Level harness, or Smartcraft recently?

If not, I would have the TPS monitored while this is occurring (to see if the TPS values are fluctuating).

[Costa Plente]

I haven't had this boat and motor very long and it is my first Mercury. I have talked to you before about the SC 2000 and was looking into upgrading to a Mercury monitor however the motor is a 2002 and that system won't work unless I change out some expensive parts. When I got the boat and was checking it out I noticed that the SC 2000 wasn't working and I found that the harness was not plugged in so I connected it and did a reset. Could the SC 2000h be bad and is what causing the problem ? Does the SC 2000 have to be connected for the motor to run right or can I just unplug it.

[EuropeanAM]

Simply unplug it and see if the problem persists. It is not required for the engine to function (it's merely a display for information).

[Costa Plente]

I disconnected the SC and took it to the lake for a test run. It still does not idle the way that it should. While it out of gear the RPM increases and decreases on its own and now it seems that the tachometer in the consol has gone crazy and isn't reading correctly. It just started this so now I don't know what is going on.

[SilverFox579]

Could be the tracker valve, wait for Don to advise.

[EuropeanAM]

It would be a good idea to check for liquid fuel in the AIR side of the system. Also helpful to check AIR and FUEL pressures, and record results:

-At idle
-Under Acceleration

-5/10/15 seconds after engine shutdown (restart for each time period).

[Costa Plente]

I need to buy me a real good shop manual for this motor. Can you give me a recommendation for one.

[SilverFox579]

Contact Rhonda with your engine serial number, none better and BBC member discount too.

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