2001 Cadillac Deville car is dying

I have a 2001 Cadillac Deville. Sporadically, it will die. Sometimes at idle and sometimes at 50 mph. The rpm's are not holding at 700. Sometimes they drop and it dies. Sometimes they will stay very high when I let off the gas. Drop to 350rpm and die or stick at 1500rpm when stopped. I have replaced the air control valve twice. I can find no vacumn leaks.This only happens occasionally and the check engine light does not come on. When it did it indicated that the air control valve was the culprit. The air control valve is controlled by the kmm, correct? Is that the culprit, it is very expensive to replace/