If you have EHC2 on an 03 model, you have a very early version of the system that became standard on the 4.8is. The control module is usually at the root of all problems. The older modules (until mid year 05) were all problematic. You should find the latest version of the module, part number ending 999 and swap it out. You can calibrate and play with sensors on the old units until you're blue in the face and it won't work right.

__________________
2003 4.6is built June 27th, 2003
2004 4.8is built June 6th, 2004