May be the crankshaft position sensor. Is it ever hard to start, like cranks over and over?
When I had a bad one on a 4.6, it would crank over and over and the tach would read 0 instead of 200 RPM while cranking. Then other times it started right up.
97 T-Bird LX 4.6 - 80k miles
94 Supra TT Auto - street/strip car
04 CVPI- Brenda's car - 76k miles
95 T-Bird LX 4.6 - fully optioned, owned 15 years, 220k miles
96 Cougar XR-7 4.6- Brenda's car, owned 11 years, 187k miles
88 T-Bird 3.8 - first T-Bird, owned 5 years, 206k miles