Changing the timing always gave my car a bad hunting idle problem also. You have to play with the idle screw and the TPS after you mess with the timing. Or atleast I always did.
Sky
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-1989 Saleen Mustang #406- TFS Heads, E-303, edelbrock intake,70MM TB, 73mm MAF, off road H, headers and 3chamber flows.
12.55@107mph
Runs on 87 Octane and gets 24mpg!