Most of the time my clutch will engage higher (foot farther off the floor), but once in a while it'll engage way sooner (much closer to the floor) and I'll be caught off guard and stall the bugger.
id try bleeding the system the other thing i can think of is there is a spring behind the piston in the master cyl sometimes they break and can cause funny business like this..
usually that happens when either the master or slave is leaking.....
there's no spring in the cylinder itself (well, there is one behind the piston in the slave.... but i couldn't forsee it breaking.... just getting weak), there's a spring on the pedal... but the "springing" back action is by the spring on the pedal and the pressure plate....
I'm getting a similar problem in my 1990 sedan (not the GTS, it's perfect). Except that it doesn't fully engage at different pedal heights, it simply "phantoms". Meaning: when I release the clutch, sometimes it begins to engage early (almost on the floor)--but then the engagement stops. It's enough to make the car roll forwards slightly, but after a brief moment it disengages again on its own...I was puzzling over this and wondering if a faulty throw-out bearing could do this. But I guess it couldn't, so it must be one of the cylinders...