a few years ago i had a problem with my couger, and it too sounded like a helicopter. the problem was one of the spark plugs game loose and popped out. it ran really rough, cause of the 1 less cyl. not sure if thats your problem though, good luck!
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89 GT AOD w/ shift kit, B&M rachet shifter, Trickflow intake, Crane (E-type) cam, 70Tb, 75MAF, 1.6 Rockers, Pulleys, MAC headers and H-pipe, Dynomax mufflers, K&N, 3 core radiator, white face gauges, custom interior, cobra R rims
MY89GT