Problem with idle speed!

[Pegasín]

Hi!

Remember in past messages, I had an electronic failure in my engine and the Hall sender from distributor was the cause.
But since this, (3 months ago) the idle speed it's goes "crazy".
I'm try to explain this:

Sometimes, when I stop the car, the rpm's goes down and goes under
intermittently. For example, like when I arrive to a red traffic ligth or I'm parking. It happens sometimes, not ever and it's more frequent at cold temperature.

If I accelerate a bit in neutral the idle speed stabilizes correctly.

But this happens with the warm engine too, but it's less frequent.

At the moment, I cleaned the air control valve (ref. 048 133 455 ) and the engine goes better but the failure continues.

which may be the cause?

Thanks for your help!!!

[Pegasín]

Another question:

I thought air valve opens at cold temperature...

...but yesterday when the idle speed was wrong after a long travel, I remove the pipe from air filter box and I note that there was vacuum (it means that the valve is open). I covered the pipe with a finger and the engine stopped...