Canon 24-85 autofocus problems

I have this lens http://www.amazon.com …2-8174708-1372936?ie=UTF8
and have been experiencing some autofocus problems. I used it last weekend with no problems but when I returned home it only hunts in autofocus regardless of which focus point is chosen. Occassionaly it will lock on a point but will still be out of focus. I cleaned the contacts off with an eraser but that is the limit of my fix it knowledge. Is this a send it in kind of problem or does anyone have any other advice to offer. note: I also tried it on a different body and it didn't work their either.

And how much EV light was available to focus at home?
Bright outdoors or darker indoors?
Aimed at low contrast or high contrast subject?
Which body? AF is function of lens and body together.

It's a nice lens, but it's not f/2.8, so it will hunt on low contrast subjects in low light. Any f/4 lens will, even the vaunted 70-200 f/4L. So will a $4,000 camera body. Passive AF is not magic.

I tried in various light conditions with various levels of contrast. It was used in similar light conditions before with no problems. The bodies were a 20d and 300d.

Does the lens do nothing, or rack back and forth hunting?
Doing nothing: Check to AF/MF switch.
If it's racking, and camera was NOT set on AI Servo, and it was new, maybe it's up for a trip to Canon?....
I've busted my share of gear. I bought one of those 24-85s and use it for photo essay knockabout work. Never broke it. I've broken L lenses though. Go figure.
J

Thanks for the help, it looks like it may be taking a vacation to canon.