Hello! I have an idle issue iv been trying to nail down. Every once in a while while I'm driving the idle will change from the normal 750ish to 2-3000 (tach is broken). It used to surge then I replaced the IAC valve and that stopped. Things that may not effect it but iv kept in mind is a slight missfire causing stepped deceleration and very faint stepped acceleration as well as a slight exhaust manifold leak. I understand that the manifold leak screws up fuel injection from the incorrect O2 feedback but I'm not sure if that would effect idle rpm that drastically or at all. Any advice is appreciated! Thank you!