[scarceller]

Very interesting that when you hold the clutch down is when you get the problem. I suspect that the pedal cluster may be lose or flexing and actually pulling on the throttle slightly but just enough to pull it off idle.

This should be easy to check just have a helper depress the clutch while you look at the idle switch in the rear.

Maybe your pedal cluster is comprimised (cracked and weak) or maybe just loose, meaning not properly mounted to the floor. I would check this out before hand.

As for your idle adjustment you should never adjust the screw without b&c jumpered. Set the idle to 800-825 and that's it.