2020 merc 300 proxs intermittent high idle issues

[dbs1]

Ser#2B738684. A few months ago it did this and the dealer claimed I had a coiled cord hanging too close to the hot foot hanging it up. Not sure about that.
It did it again a few days ago a day after a long distance rough ride. Starts up and idle goes to 1200-1400 rpm and doesn't come down. Hit the throttle a few times, turned it off and no change. Started again, Slid it in gear, which was unpleasant and then it would only rev to 2500 or so and not go on plane. 70 miles from the ramp had me thinking of a long swim.
Turned it off and waited a few minutes and back to normal. Checked for any interference with the hot foot and nothing there. An hour prior I had managed to get a line wrapped around the prop upon start up and we quickly got that undone but don't know if that's related.
Ideas?

[thommo59]

Maybe possible your battery is going out and these engines will automatically raise the idle to assist in charging. Just a thought

[dbs1]

Battery is only 3 months old and showing full charge, but one never knows, and raising idle to the point of chunking when going in gear can't be good along with limited power in go mode. Luckily it didn't last, but I'm sure wanting to figure out the cause.

[thommo59]

The limited power sounds like a guardian mode but not sue I would be keen on putting in gear at those revs.

[EuropeanAM]

This is very likely a DTS problem- your limited engine RPM's tend to indicate that there is a fault occurring and the engine is in GUARDIAN.

Possibly a problem in the ETC (Electronic Throttle Control).