question about idle and rpms and smart craft gauges

[mikepags]

I have noticed from watching the smart gauge that when I idle in gear (2006 250xs) that its constantly changing and the range is big enough to make me wonder why..... an example would be 580,620,600,620,540,600,580,560.or somehting like that......the difference from the top of the range to the bottom is more than 10%.......I haven't watch it enough or paid that close attention to see if there is a true pattern or if the numbers go in order from highest to lowest and just keep repeating or if something should be adjusted or checked........I didn't know if it could be one spark plug isn't firing as well or who knows what I can only guess ...........with any amount of throttle it will hold the rpms to with 20 or stay constant which again is what me wonder about the wide range at true "idle" in gear................Yes I spend to much time idleing but I want to keep the XS attached to my boat and not talk to my insurance agent

[EuropeanAM]

RPM variances at idle (especially in gear, running a 25P or higher prop) are quite common. Idle speed is "controlled" digitally by manipulating the ignition timing.

This will result in "some amount" of RPM hunting... although it is usually over a 25-100 RPM range. Despite the readout, you should not "perceive" that the engine is "surging".

There are several items that can be checked on this.... one of which is the throttle plate opening clearance. DON'T just "arbitrarily" adjust the throttle plate- the ECM was calibrated for a "specific" air gap at idle position.

First, make certain that your throttle cable is returning fully against the idle stop. Next, utilizing a drill bit, see what size bit is the largest that will fit between the throttle plate and the throttle bore. Once you have this figure.... feel free to give me a call. I'll make a comparison of my notes...

[mikepags]

"RPM variances at idle (especially in gear, running a 25P or higher prop) are quite common. Idle speed is "controlled" digitally by manipulating the ignition timing.
This will result in "some amount" of RPM hunting... although it is usually over a 25-100 RPM range. Despite the readout, you should not "perceive" that the engine is "surging"."

Thanks Don..........that was what I was looking for.........