You are going to have to give us more than "I noticed on the engine there looked like a screw was missing". There aren't any screws on our cars that are NOT needed for something, or they wouldn't have been there to begin with.
How about a picture of where you think the screw is missing? You'll probably have to post 5 or so comments before the forum will allow you to post pictures, so get started!
2005 300C BRILLIANT BLACK, DRL, Mesh Grill/Vents, Chrome Pillars & Fender Trim, MDS Indicator, Quad Brake Lights, Tinted Windows, De-Molded, K&N Aircharger, 180 T-Stat, Flashing Sidemarkers, Predator Cust. Perf. 93 CAI Tune
1997 MUSTANG COBRA 'VERT, TRIPLE BLACK, Vortech S/C'd., ECT Mod., 4.10 Rear, 18" Saleen Wheels
1950 FORD TUDOR FLATHEAD V8, FLAT BLACK, 54 Chevy Grill, Nosed/Decked, Frenched Headlights, Air Shocks, Three-On-The-Floor w/OD, Dual Glasspack Exhaust, Dual Two-Barrel Carbs