What was the solution here?
I have a similar problem with a GTV 1.8 ts 16v.
This car has the issue for a very long time allready, if you start the engine cold it turns 1200 rpm or so, it warms up and the rpm goes to 800. No problem, but if you go driving and push the clutch, the rpm drops completely down, then goes up and so further. Sometimes the engine stalls, sometimes it's like you don't have it, really strange.
With a distribution belt change last week I also changed the intake variatior on the intake camshaft, I tought it maybe was causting this, (because the last month's the engine didn't run wel anymore higher then 3-4000 rpm).
But It didn't help.
I found another problem, the rubber inlet hose was cracked at several places, replaced it, but not a solution.
Then with a read out of the fault codes I find that the camshaft sensor on the exhaust cam is bad. Replaced it, idle issue isn't solved but the engine runs a lot better in higher revs.
Now I'm thinking the issue is maybe the maf sensor but i'm not sure yet, tomorrow I will try.
At idle when it's going up and down you can see the butterfly valve turning, so it works, but not enough i think, it turns well by hand so I don't know what could be wrong there.
Hopefully anyone knows the cure.