any odd place where a vacuum leak may occur

i still have the high idle problem, i would like to know if anyone would know of a place in the car/engine where a small vacuum leak could occur in a 1993 mustang gt vert. i have search throughout my car and found no leaks, but i have checked everything to be the cause of the leak, but i get good vacuum pressure @ -18psi, stock is -15psi. This is the only thing left that can cause my high idle. i appreciate any help.

yes, im sorry, i forget the vacuum is measured in 18" of mercury. that is my vacuum pressure, but i have done almost all other things to fix the idle problem. i have switched out the MAF sensor, replaced half of the vacuum hoses, and checked them all, i have sprayed the gaskets with carb cleaner looking for a leak. i have bypassed the charcoal black box to test for a leak there. with no success. i have cleaned and checked the IAC by removing the IAC and pluging the holes of the IAC, and the car idled normally @ 700rpm, i was told the car should die or be near to dying, but it never got close to that. so i conclusively figured it must be a vacuum leak problem. the idle set screw is set where the blade in the throttle body is just out of the range to stick on the aluminum. the idle problem persist and i am being driven more made every day. could it be a problem with the thick film integrated ignition, i woudnt think so though. if anyone has anyother suggestion on how tho fix the problem, please tell me, i have done all i know to fix the problem. when i run koeo, i recieve no codes, but with koer i recieve a code that states the idle is too high and nothing else.

if you could, please give me some more info, i live in edmond oklahoma, and i have been dealing with this for about 4-5 months now, the problem occured the same time my MAF sensor got clogged with dirt and ther car began to backfire continuously at all RPMs. i have replaced the hose going to the the emissions canister from the front of the upper manifold, but i havent taken the manifold off. if you would please give me some more info, i would really, really appreciate it. i have already spent about $700 on misc parts for the backfire problem, which turned out to be clogged MAF, and everything else that could cause idle and lean fuel problem, or backfire problems, autozone usually helps alot, but the mustang genius i have talked to cannot put a finger on it. i couldnt be more thankful if you were to tell more about your problem and the solution, please i beg you.