int backwardsScan = 0;

    ...

    case 3: // KITT-like scanning back and forth 90us/1us
      // j remembers which LED pair is active
      // backwardsScan remembers which direction to scan
      // timer4 handles the 90ms/1ms on-off cycle.
      // 
      // reset output leds appropriately for (j,timer4):
      for(int ii=0,ii<=5,ii++){
        digitalWrite(ledArray[ii],( (ii==j) && (timer4 <90) }
      }
      // update KITT state based on (j,backwardsScan,timer4)
      if(timer4 > 91){ 
         j += backwardsScan? -1 : 1 ;
         if (j > 5){
            backwardsScan = 1;
            j = 5;
            }
         if (j < 0) {
            backwardsScan = 0;
            j = 0;
            }
         timer4 = 0;
         }

      break;