High idle speed

[oscarloco]

Hi guys

Nice to see the forum up and running!

Now, my ZX has a nuisance, the idle speed is a little high (1000-1200 rpm). It stays there for a while and then goes down to normal. Sometimes it does it, sometimes it doesn't and that's the point. I tried lowering it with the throttle stop screw but it doesn't.

And if I turn the screw the other way to raise it, it becomes erratic: raising to 2k and then going down to normal (but sounds like the engine starts to die and then goes up again) and repeating itself.

Now, the conical gasket in the exhaust to manifold joint is worn and my theory is that oxygen is getting in thru there, effectively fooling the oxygen sensor. I come to this conclusion based on fuel economy, as it is consuming more fuel than normal.

Any ideas?