[928uk] Clutch question

[Daniel Weston]

Hi all, firstly thanks for the help with my A/C question a few weeks
ago. I've not managed to fix it yet but its on the list of things to do
before a long trip top France...

I have a late (J-reg) GT which has now done 105,000 miles on the
original clutch. I have no reason to expect that it is getting worn, but
my feeling is that it can't last much longer can it? It has a slightly
squeaky thrust bearing (i.e. touch the clutch pedal and the squeak goes
away) but that is liveable with. The clutch is pretty snatchy/jumpy when
trying to pull off slowly. 

My question is, when a clutch begins to go, over what distance will it
typically become unusable? I am planning a couple of thousand miles over
the summer and I really don't want to get stuck in need of a clutch. Am
I just being paranoid or should I get it replaced sooner rather than
later? 

On another note, I notice that the car's idle speed is not 100%
constant, i.e. it fluctuates by a few hundred RPM, sometimes when
declutching the car seems to "blip" the throttle. Is this the idle
valve, and it so are they a DIY replacement?

Thanks in advance.

Daniel