I believe you want to look at the property dropDownWidth
However, depending what you're doing you may want to take a look at the Flextras AutoCompleteComboBox. We have two properties you may be interestd in.
ExpandDropDownToContent will expand the drop down to fit all the largest item no matter what the width of the ComboBox is.
And truncateToFit will truncate the selectedItem's labe and show a tooltip with the full item. Labels already work this way:
I hope this helps.
Thanks for the Reply
The e-mail I got had more text than your reply here.
I haven't looked at the Yahoo AutoComplete. But, if it is based on the ComboBox, the dropdownWidth property should apply.
For the Flextras AutoComplete if you want to turn it into an AutoComplete TextInput , as opposed to an AutoCompleteComboBox, you can use the downArrowVisible property to remove the down arrow from display.