I am thinking of replacing the cables
a; because the bike is 14 years old
b: bmw says replace at 30 thou or so, I have 109 thou KM
c: I do not like the risk of a broken cable.
Having said all that I am just wondering if the PO had changed cables and in the process bent a bracket to cause the fast idle.
Is this a reasonable possibility?
I have done a lot of work and testing related to the Throttle-bodies adjustments - including checking errors with GS911. I have also swapped TB-assy and opened them for cleaning and inspection.
In my opinion, if nothing as ever been opened or removed (TB-assy or cables) most high idle condition come with age caused by intake air-leaks after 5 to 10 years. Often related to small vacuum hoses, rubber intake tube between cylinder-head and TB-assy, or O-ring under intake manifolds.
BUT... in real-life, most often something has been opened or removed for maintenance. In such case, much before the age of rubber components makes it as problem, I find the throttle-cable(s) free-play to be the main issue causing problems. If the throttle does not snap back completely closed (with some free-play at handle-bar), the Motronic-ECU gets confused because it sees a higher TPS at rest when ignition is turned ON.
So in order of easy to more complex:
(1) make sure you have free play as documented in shop-manual (or Clymer)
(2) make sure the throttle-close is positive and consistent. If cables feel stiiff and do not come back normally, better to replace in garage than on the road ;-)
(3) inspect small vacuum hoses (maybe loose , or a leak). As suggested before, just plug all of them or the nippples on TB-assy to eliminate these as potential cause.
(4) if you have acces to GS911, have a check for TPS base setting (this requires to remove TVA - also called idle actuator)
I will not explain the TVA (idle-actuator) check as it would take a fairly long post with picture. Easier to start with the "most probable" list above.
Last, but the least of a job, you may need to replace TB-assy related rubber parts described above, if you cannot find a solution with the easier stuff listed. If you have to go there to install 2 new throttle-cables (pull cable and return-cable) , you might as well do the rubber parts at same time. Once all that is done, you are good for another 8 to 10 years unless you do 25,000 miles each year ;-)