Soft clutch pedal only when engine is on

I'm having a weird issue with my clutch pedal and have run out of ideas.

 

Initial symptom was a very soft clutch pedal. I tried bleeding the system but could never get it to build up pressure so I replaced the master/slave cylinder. (at the time the pedal would not even return under its own power).

 

Now I get a firm/normal feeling clutch pedal but only if the car is off. If I start driving it almost immediately goes soft. Everything seems to engage and shift fine, it just has a very soft pedal.

 

I have also replaced both the hard and rubber hydraulic lines with no luck.

 

Has anyone seen this before?

If all the hydraulics in the system are new and properly bled, the only other thing I can think of that would affect pedal effort would be the pedal assembly and the pressure plate.

 

As you state the problem occurs when the engine is running. This has me leaning towards the pressure plate, however, I have no idea how it would cause what you describe. Have you recently had any clutch work done to the car? Stock pressure plate?

i have a similar issue on my LGT, but if i drive and start shifting at higher RPMs... it seem to get stiffer. My clutch engagement point also changes depending on how i drive. Let us know what you find out. I have also change out my master and slave cylinder and bleed it several times with the same problem.