Rough Idle

Last seasons' last ride where bike started to have a rough idle. Online research found that most common cause is a bad coil.
First, could there be any other common cause?
Second, how do I test to find which one is bad?
Third, should I just replace all or just the one that is bad?
Thank you for any input.
Patrick

There are several possible causes of rough idle, ranging from a "bad coil" to bad gas to a bad spark plug wire to a partially clogged fuel injector, to .... and on and on. Knowing the model and year of the motorcycle would help us decide how best to troubleshoot the issue.

rough idle

apologies for not including bike details, I thought that somehow it would be included as part of my profile information.
Mine is a 2006 R1200RT with about 80,000 kms.
There was no noticeable difference in the engine performance during that ride and only showed itself when coming to an idle at an intersection in town.
The fuel pump mounting ring recall had been done earlier in the year without change, though it still smells of fuel as always. I attribute that to my decision to add fuel to the neck of the tank to ensure maximum distance between fills. Has never posed a problem before and I don't believe it to contribute to the rough idle. Fuel used was same as the majority of fills using a premium grade major brand fuel. Oil used is, from new, organic Castrol 20W50, which I realize should have no impact whatsoever on the idle, just more info.
It has been an intention of mine to change out all of the spark plugs for some time and was going to research coils and wires prior performing the work to see what public opinion may hold for such a change. Heavier gauge wires, 'hotter' coils, though an improvement for hot rods may not have any effect here especially with the coils being almost model specific. I see that 'Beemer Boneyard' carries a brand that they state were the OEM supplier of coils and am considering a complete swap along with plugs. I also doubt the altitude where I live and the frequency of travelling to sea level and back would have any effect with the modern electronic engine management. Engine temperature gauge always reads virtually the same no matter the ambient temperature unless stuck in traffic where it may increase one bar on the scale.
Further to my problem, please allow me to thank you Paul for your efforts and wisdom. I was pleasantly surprised to see that you had responded to my query. I have read your column with great interest over the years whether or not I had any knowledge of the era or model of bike you were describing as there are always tips and tricks to learn from experienced hands such as yours. Perhaps one day our paths will cross and I will be able to thank you in person.
Patrick

patricio66 said:

The fuel pump mounting ring recall had been done earlier in the year without change, though it still smells of fuel as always. I attribute that to my decision to add fuel to the neck of the tank to ensure maximum distance between fills. Has never posed a problem before and I don't believe it to contribute to the rough idle.

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If you are regularly filling your tank to the brim, you may have saturated your charcoal canister, causing an overly rich mixture = rough idle. It is not normal to smell raw fuel.

Fill only to the bottom of the filler neck unless are going to immediately ride twenty miles or so.