My car has the EXACT same problem. Its had it since the motor was put together w/ the heads,cam,intake. I hve tried everything to figure it out. It almost feels like a loose drivetrain, so I checked all that stuff, put in a new driveshaft, motor mounts, and transmount etc.
If you EVER Figure it out, PLEASE LET ME KNoW! About 2200 rpm or so it runs fine right?
Skyler
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-1989 Saleen Mustang #406-
TFS TW Heads, E-303, Edelbrock intake, 70mm TB, 73mm MAF, 24lb injectors, 1 5/8 shorties, Off Road H, 3 Chamber flows, Jaz Race seats, Back seat removed, sub-frames, Roll Cage, and a 80 shot of N20.
12.54@107.4 Motor
332RWHP, 350rwtq