well while i was at the track last night i talked to a few guys with mustangs, and one recommended that for my surging to drill a 13/64 whole in the throttle body... i know this would be considered "patching" the problem, but ive tried everything...
ok here it goes: replaced EVERY vacuum line on the car, three new IAC's, ford air adjuster, 2 TPS's, Tried every voltage KOEO for the TPS with no luck, tried timing, reset the computer bout a billion times, replaced all the gaskets from the lower to heads and the lower to upper, and im sure there is more... after i reset the computer, it idles almost as a B cam... its acctually quite nice... then out of no where it just starts to spaz out an surge about two weeks later... o and ive also tried a new computer...
I don't recommend drilling out the throttle body because you usually end up with a whistle at part throttle. E cams don't like to idle below 900rpm or they get to surging. What I do is close the throttle plate until just before it binds and reset the TPS to .98vdc and the timing to 14 degrees BTDC. Then remove the IAC and using a dremel or die grinder cut a groove between the air ports (kinda like the idle controller Ford sold for years, but more effective with bigger cams. I start with a 3/16" half round port and try that after blowing out the IAC. Let it warmup and check the idle, making sure it's at least 900rpm, but better at 1k. If not open it a little more. Usually I end up around a 1/4" groove and the car drives much better. With the TPS set with the throttle closed you enter WOT earlier in the throttle sweep and the car feels more responsive.