Try this out, sometime ago i faced same problem and came up with this it might work for you
function SearchText() {
var cache = {};
var oldterm;
$("#txtItem").autocomplete({
source: function (request, response) {
if (request.term.indexOf(oldterm) >= 0) {
if (typeof (oldterm) != 'undefined') {
var data = jQuery.grep(cache[oldterm],
function (ele) {
return (ele.indexOf(request.term) >= 0);
});
response($.map(data, function (item) {
return { value: item }
}))
return;
}
} else {
cache = {};
$.ajax({
url: "JobTagPricing.aspx/GetAutoCompleteData",
data: "{ 'item': '" + request.term + "' }",
dataType: "json",
type: "POST",
contentType: "application/json; charset=utf-8",
dataFilter: function (data) { return data; },
success: function (data) {
oldterm = request.term;
cache[request.term] = data.d;
response($.map(data.d, function (item) {
return {
value: item
}
}))
},
error: function (result) {
alert("Error");
}
});
}
},
minLength: 3,
select: function (event, ui) {
if (ui.item) {
formatAutoComplete(ui.item);
}
}
});
}