Idle /w clutch problem
 

Maybe you guys could give me an insight on this. I been trying to solve this my self, doing some electrical testing following shop manual by i can't seem to figure out the problem.
Okey, everytime I start the engine. I have to hold the clutch on the floor so the engine will do its fast idle until it gets down to 750RPM. If I don't do this especially when its cold (or first start of the day), once I turn the ignition key on, the engine would rev to about 3000 and will quickly dive down to 750 or lower and eventually die (after some seconds or so). Also, if the engine has warmed up, and sitting is sitting at 750, if I pressed the clutch down, the tach will go down to around 600-650.
So, hopefully you can all understand what I mean. And I hope you can point me out to the right direction.

I got a 1988 N/A engine.

The thermowax device and fast idle screw and cam are out of whack. Needs adjusting. Or someone has done what they call the throttle body mod and screwed up your car imho.