z3100 - carriage pausing problem = slooow printing

Hi,
I believe this was discussed before but I'm still unable to find a solution.

Printing on 44 inch Fredrix 901
The problem I'm having is that the carriage assembly makes one print pass then pauses at the left side to clean? or read the edge? (not sure) this takes a few moments then prints one more pass and repeats the pausing. It takes almost an hour to print 6 inches of a 20x30 image.
What's causing the slow down? Is there perhaps dust or dried ink on a sensor somewhere on the carriage?

Hope someone can help
Thanks
Andrew

*Update
Perhaps a data transmission problem? I'm connected USB using a Mac G5 (2 gigs of memory)
Will restart computer after printing to check connection

***
Problem resolved
It was a data transmission problem from the computer. Prints normal after restart.
Glad I finally figured it out. This was a constant problem