I have a friend who has a 580rwhp 96 Mustang Cobra and his car wouldn't idle (surged until it died and also did the bucking you're talking about). He got the programmable Ford Motorsports Computer and since then (after getting it professionally programmed) the problem dissappeared and the car is very drivable now. Good luck, i hope this helped some.
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'84 Mustang 5.0 T5, FMS aluminum radiator & 180* thermostat, 1 5/8 shortys/2.5" duals, '88 GT tail lights and wheels, Holley 4160 4 BBL, smog pump idler, now with hi-po collapsed lifters in #3 or #4
