Really weird things going on. Car idles just fine when sitting but as soon as I engage the clutch even if I'm in neutral then the idle drops down. Does anybody have any ideas ?

This is a total WAG, but might it be a throw-out bearing that's gotten stiff causing a rotational load on the pressure plate? Can't think of anything else off hand that would cause such a condition.

Edit: I noticed down the page a bit a post with a similar condition, it appears that his arm was rubbing the pressure plate....well, it's something else to check at least.

Clutch tube loose in tunnel and cables hitting each other?

clutch cable and throttle cable tangled?