I have an 88 5.0 coupe speed density. Recently i set my timing, TPS, and put new distributor cap, rotor, wires, super coil, and plugs in. When i pulled out the old plugs there was a small bit of oil on the plug threads and signs of burnt oil on the diodes. There is no smoke out the exhaust. When the car is cold only when I rev her up she backfires,and its not just a small pop, its very loud and irritating but when im driving she runs very strong and smooth. The plug gaps are set to the proper specification as well. Are my valve guides worn out? Piston rings mabey? Please help. Theres only 161k on the car and shes stored away every winter. Thanx for your time!!