TSOJAN

Hi guys, i just bought a s2000 2 weeks ago. The car is a 2002 model, has done 39k miles and was imported from Britain. This is the first time ive own a sports car so im not sure if what i feel is right. First of all, the car has a tapping sound from the engine, while staying still and releasing the gas pedal to hear how the engine sounds, the rpm drops down below 1000 and almost stops the engine. The car runs smoothly in the lower gears but when i take it to the highway doing 80 to 90 mph in 6th gear the car seem to vibrate quite alot. Also the engine bay is a disastor, theres brown and yellowish oil all over it, the engine paint is also peeling off. I geuss the engine has been rewired before by the looks of the wires. I really hope theres nothing serious, if so is rebuilding the engine a good option?