Check your EGR valve and its operation. There is a solenoid that controls vaccum to the valve and it may be malfunctioning or your EGR valve may be seized (If you look at the diaphram of the EGR valve while the engine is idleing and goose the throttle you should see a slight movement in it).
The EGR valve vaccum solenoid also has a small air filter in its top part, check it to see if it is clogged.
If your EGR checks out okay then check the TP voltage (should be somewhere around .85 to .99 volts KOEO I think)
That's all I can think of right now hope this helps.
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1968 Fuel Injected Mustang Coupe
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