Sounds more like a vacuum leak, or missrouted vacuum lines. There is a bulliten for hesitation, as follows:
5.0L ENG TIP-IN HESITATION - DIAGNOSIS/REPAIR TECHNICAL SERVICE BULLETIN Reference Number(s): 85-23-12, Date of Issue: November 21, 1985 Related Ref Number(s): 85-23-12 ARTICLE BEGINNING HESITATION - 5.0L H.O. - ON TIP-IN APPLICATION Model(s): FORD : 1985 LTD, MUSTANG LINCOLN-MERCURY: 1985 CAPRI Group: Engine Bulletin No: 85-23-12 Date: November 21, 1985 Calibration 5-22A-R00, 5-22P-R00; 4-22A-R00, 4-22P-R00 SERVICE INFORMATION To service customer concerns of tip-in hesitation during light part throttle accelerations, check: vacuum hoses, EGR valve and solenoids, ignition timing, T. P. Sensor, fuel pressure and the EGO sensor and wires. 1. Perform EEC IV Self-Test using Rotunda Star Tester No. 007- 2. Verify all codes and service as necessary (Refer to TSB 85-20-6 for occurrence of service code 42). 3. Check for vacuum leaks and restrictions (especially in MAP sensor and EGR vacuum/vent hoses). The hose connecting the EGR solenoid to the EGR valve is routed in :he vacuum harness and cannot be readily inspected. Replace it with 5/32" I.D. Vacuum hose. 4. Check for grease inside EGR solenoid hoses (control and vent hoses). Replace vacuum hoses if there is evidence of grease. 5. Check EGR valve for sticking. With a hand vacuum pump, slowly apply vacuum to EGR valve. If pintel does not move or appears to be binding or sticking while lifting off seat, replace EGR valve. 6. Check ignition timing and set to specification. Refer to Vehicle Emission Control Information Decal. 7. With idle speed set to specification and throttle closed (dash- pot collapsed), check throttle position sensor voltage between pin no. 47 and pin no. 46 (green and black wires at TPS). If Press Ctrl+F to find exact text voltage is below 0.8 volts or above 1.2 volts, adjust TPS sensor to 0.9 volts. 8. Check fuel pressure, if above 43 psi or below 39 psi adjust to 41 psi. To adjust pressure, remove air cleaner. Remove tamper resistant plug from pressure regulator and turn Phillips screw 1/4 turn. Recheck pressure. 9. Check EGO sensor and wiring. A. 1985 Mustang/Capri (calibration numbers 5-22A-R0, 5- 22P-R00, 5-111-R00 only): Verify exhaust gas oxygen sensor is heated. (Heated sensor has three wires.) Verify EGO heating circuit has a fuseable link and is connected at left hand apron near dash panel. (Fuseable link is purple.) B. 1985 Mustang (calibration numbers 4-22A-R00, 4-22P-R00 only): Check for correct EGO sensor. It should be non-heated (single wire). 10. Verify all hose and wire connections are secure.
2/14/2010 . Check vacuum leaks this way.
Get a can of spray Throttle body cleaner, start the car and spray around, pay attention to vacuum lines and manifold, if the idle changes, you found a leak. You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!
Keep the spray away from the exhuast manifolds.
Sunday, February 14th, 2010 AT 9:43 AM