Strange problem with Wireless Intel 3945

hello, I have an Intel PRO/Wireless 3945ABG card and I’ve got a little problem. Sometimes the connection goes bad, very bad, and I discovered that if I unplug the AC adapter (which is connected full time) automatically the connection goes stable. I can connect it again, and it will work normally.
I don’t know what can it be. It’s not very serious, but it’s a little annoying.
As soon as it happens again, I’ll post the /var/log/messages out.

Someone has experimented this problem?
Thanks in advance
Sorry for my bad english