hey:
in your Arduino program, make sure you put a delay between printing the integers of your sensor.
So you would you have
printByte ('A');
printInteger (sensor1);
printByte (10);
printByte(13);
delay (20);
printByte ('B');
.......
The delay function is so Max, (as well asd Pure Data) can process the information. You might want to experiment with the delay (value) to find the duration that is fast but not too fast.
-nima at sfu