I have had a look through some past posts and have found some things to check.

K100RS 1984. Generally runs well, POs (including present one) have been tinkering.

Typically, inconsistent idle until motor fully warmed up after about 20 mins of riding. My thoughts were throttle body mounting rubbers leaking. Tried the "spray with something inflammable" (also used butane) - but no difference noted. Recently though, idle has got worse.

Read somewhere that the coolant temp sensor might be an issue. 
In the process of getting at CTS, I deoxited what I could get at and generally cleaned up...

Noticed that air filter top box did not have blanking grommet and installed one. (Q: will putting one on have any major effect on the idle of the bike?)

Noticed that Throttle body mounting allen bolt near CTS was easily turned another 1/4 turn... so pulled throttle bodies out of mounting rubbers and tighten the lot. Resisted the urge to get them onto the bench and thoroughly clean. (Q: I have really only pinched them tight. Can too tight create an air leak? I am thinking that I should redo the spray to check for leaks. After that, maybe remove, make sure they're flat (very fine wet and dry paper on flat surface eg glass) and renew o rings (vitron)). Then I'll be reaching for some black mastic or similar)

Installed CTS. Slight improvement but still unsatisfactory. Though choke seemed not to be working. Will confirm cable is correctly housed (it worked fine previously). As it was getting dark the mozzies drove me indoors.

Subject to further checking:
plugs are relatively new, HT leads old but deoxited and cleaned, crankcase vent hose 4 months old, fuel new 98 Octane, fuel lines (in tank) all tight and correct, injectors clean (filters and o-rings replaced 4 mths ago, cleaned out) and properly in position, battery fully charged and about 2 years old, sprag clutch continues to taunt me...

PS
Radiator fan is not correctly wired in. PO has linked into wire from CTS - probably for handlebar switch. Now there is a loose wire to either be reused or removed. (Q: where do the two wires (violet/yellow and brown go to? I assume brown is earthed to frame.) My electrical knowledge is limited, but I would have thought the temp sensor relay would supply power to fan when trigger by CTS (but then I'm reading CTS send signals to ECU and hence affects fuel injection and idling??)

PPS: the hit list is: check choke action, are any TBM clips fouling the movement, recheck crankcase hose, check plugs and clean, clean TPS electrical connector, check for leaks at TBMs, maybe replace injectors with serviced ones off another bike, remove blanking grommet from air filter top box (or find Martin's mixture test / technique on this forum)...

Any help greatly appreciated

Regards

Guy

How long since the last time you checked valve clearances and throttle body balance?

As per .75 plus check the mixture. When your bike has been warmed up and at your normal idle speed press the green starter button. If the mixture is correct the revs should stay the same or rise only very slightly. If the revs rise significantly the mixture is too lean if the revs drop it's too rich. To correct the mixture requires using the lean drop method or using a exhaust gas analyser. Adjustment with the gas analyser requires very small adjustments allowing time between each adjustment.
Regards martin.

Thanks Gents

Will be onto them this weekend.

20th Wedding Anniversary Wednesday - so discretion means I will probably not be tinkering tomorrow arvo.

Haven't checked the clearances recently (year ago?) nor the throttles. Seem to remember, one of the TB screws was not giving much response (which had me thinking valves might need shimming...or the TBM rubbers were leaking). However, I do have a carb balancer (X4). 

Will reply as soon as I've have a go

Regards

Guy