On the K75 zombie I'm bringing back to life the throttle bodies won't close all of the way so it runs up the idle. If I push down on the throttle bar with my finger I can get them to close all of the way and I tried spraying some silicone lubricant on the springs but no joy.

(I know it's not the TPS because I took that off and even with that removed they still don't close all of the way.)

I do have a spare set of better K75 TBs on hand that I can swap in so if there's no easy fix then I'll have to go that route.

the choke cam not getting in the way of a full return to closed ?

just another place to look

There are only a few reasons why the TB's might be kept open (to my experience). You already mentioned the TPS, then possibly wrong adjusted gas or choke cables (no play), the set screw at the front of the rack or a jubilee clip or similar on the last leg that's intervening with the "choke" cam and preventing full closure. There's nothing else as the springs on the shaft are expected to push them shut (or against the set screw). Let us know if you found it?

A worm drive clamp stickin' its head out?

What happens when you disconnect the fast idle cable? 

Does the engine have a fast idle light switch installed?

Naw, I loosened both cables. (and there's slack in the cruise control cable too)

I'll check the hose clamps but it was running fine when I sold it eight years ago so I don't think that's it.

I think maybe the springs atrophied from lack of use. 

Did the owner fool with the interlinkage screws in the time he/she owned it?  Is the blue paint intact? Could be that one of the butterfly valves is closing up earlier than the others as a result.

Nope. Blue paint still good. I know the PO and can't see him doing that anyhow.

Had that problem recently and fixed it by dumping a load of WD40 between the TPS and the TBs. The 'scissor' action pivot between the fast idle cable and the TBs was crudded up.

Mystery solved. The culprit is a sticky throttle cable.  I detached it and the throttle springs back to closed just like it should. Maybe the lining is worn, the cable is rusty or it's just old.  I 'spose I'll get a new one.  Anyhow, since it's a K75S with the TBs exposed, if it gets stuck while riding it's very easy to just reach down and push it back down with my hand.

In the meantime I'll break a Kardinal Rule and spray some silicone lubricant down the throttle cable. Silicon is pretty inert and I'll be tossing the old cable soon anyhow . . .