Last question first.....there is no way to determine the hours on the engine from the ECM. It has a fairly simple ECM, compared to newer motors.
First question last....You can adjust the idle, but you should check a couple of things first.
-Be sure that the engine is running on all of the cylinders. Do a cylinder drop test and one by one, briefly disconnect the injectors. If the motor rpm slow down each time, then all cylinders are firing. If the rpms do not slow down, then that cylinder has an issue.
-Check to be sure that the motor is coming to temperature. 160 - 182 deg F. If it is running cold, then that is an issue.
-Remove the Idle Air Control and make sure that the screen is not blocked with carbon. If so, clean with solvent, like brakekleen. While it is off, use some small jumper leads and momentarily exercise the IAC with 12v applied to the contacts in the connector. Make sure that the plunger moves back and forth. If it does not, then that is definitely an issue.
The IAC does most of the controlling of the idle. When you start the engine (without advancing the throttle), the IAC should allow extra air into the intake and when the motor starts, the idle will be somewhat above 1000 rpms. Then it slows down to about 750 rpm. If it does not idle high then slow down, there could be an issue with the IAC, the ECM or the connections in between. If it does idle high and then slow down, but the idle is still too low, then maybe an idle adjustment could help.
It is possible that one or more cylinders do not have good compression......that could be one of other causes of low idle.
To adjust the idle per the manual, you need the engine warmed up....put the engine in service mode (shorting the two connectors on the red service plug with a paper clip). The service plug is located under the ECM cover.
Disconnect the IAC and start the engine. You might need to advance the throttle to get the motor started, then slowly bring the engine back to idle.
Then you adjust the idle mixture screw on the top of the Idle Air Control.
http://www.boats.net/parts/search/Honda/Outboard Engine/1999/BF130AX LA/THROTTLE BODY/parts.html
The screw is located just below the bolt head of part #12 on the drawing.
It is not easy to get to, and it is probably covered by a thin coat of Honda paint. I have used a flexible screwdriver in the past, when needed.
The manual says to adjust the idle to 600 plus/minus 50, but you should set it at 650 plus/minus 50. In your case, on the high side is probably in order.
When finished, you need to erase the codes....since you set a code by disconnecting the IAC. When you restart the engine, with the IAC plugged in, the idle should come to about 750 rpm. In gear, in the water, it should be about 650 rpm.
The need to adjust the idle is very unusual. There general is something else that is causing the problem.
Hope that helps some, before you get the manual.
Mike