Still no luck with the Ir I see.
To disable the auto calibrate you will need to modify two things in your programming.
int scan_thresh=0;//threshold value of scanning sensor
You will need to provide a value for this variable. This will determine what distance the sharp starts to pay attention to things.
//find thresholds
autocalibrate();
You will also need to comment out the call to this function.
The scan_thresh value should be between 0 and 255. I'm not sure if the numbers get larger or smaller as they get closer. Why do you think your Ir is not autocalibrating? Are you sure that it is working? Have you tried to measure the signal line with a multimeter? You should get a varying voltage as things get closer or further away.
Conscripted