I just bought a 1987 Alfa Spider. I'm having trouble with the oil pressure gauge. I put a new sending unit in and under RPM's the pressure is about 57lbs, engine warm, but when it goes back to idle, the pressure gauge reads almost zero. i did check the idiot light and it is working properly and the only time the light comes on is when the engine is not running. i did have the pressure on the sending unit for the light checked at idle and was told the pressure is 40 psi. has anyone else expirenced this problem?