1999 Infiniti Q45 Service Engine Soon Light is on

I have a one owner car with no problems of any kind and at 80,000 miles the car had to be taken to the local Infinty dealer due to service engine soon light and running rough and smoking. The dealer said all the fuel injectors needed to be replaced at a cost of $3000.00, shortly after getting the car back the same problem occured and now the dealer found a naked wire somewhere on the engine shorting out and causing the computer to send the wrong signals to the engine. He repaced the naked wire and the car ran good for 6 months and then the same thing started happening again, this time the code said all the coil wires needed to be replaced at a cost of (you guessed it) $3000.00. This time I had an independant garage replace the coil wires and after a few weeks the same problem is back. The engine code states misfire on number 4 cylinder. The problem seems to be either fuel or electrical. The car at 60-70 mph starts to jerk as if starving for gas and at other times just runs rough at idle. Sometimes the car will run fine for a few days and then out of nowhere the problem starts up again, I am still driving the car but afraid I will be stranded at any time. Any ideals?