Albert,

The only comment that I know to offer is that, when I have seen the ACC go all over the place like this, I've seen the fan that draws sample air through the grill near the rear view mirror not working.

This small fan is in a few different locations on the various model 124's. Mine is near the glove box.

You could check it by holding a cigarette(yuk) or some other source of smoke near that little grill and see if it draws the smoke. If working properly, that fan draws air through the grill any time that the ignition switch is on.

Hope this helps and best of luck,