Mustang timing questions.?

89 mustang gt. cant get it to run right and base timing (10 degrees). or anywhere close for that matter. i have to set it to about 30 degrees for it to run ok. and before you say it. the timing chain and cam is dead on. i thought it might be the tps , which i replaced today. but its not. chances are you name it, ive replaced it but insite is useful. if i set at base timing, no acceleration and it back fires through exhaust.