Carousel judders

function Carousel(obj) {
        if (!(this instanceof Carousel)) return new Carousel(obj);
        // ..did they use "new"?
        if ( !obj.objID ) {
            throw new Error("Element id is required.");
        }
        this.theObj = adg.$(obj.objID);
        if ( !this.theObj ) {
            throw new Error("The element doesn\'t exist.");
        }
        if ( adg.GetStyle(this.theObj,'position').toLowerCase() == 'static' )
            throw new Error("Must be a positioned element.");
        this.objWidth = parseInt(adg.GetStyle(this.theObj,'width'),10);
        this.conWidth = parseInt(adg.GetStyle(this.theObj.parentNode,'width'),10);
        if ( this.objWidth <= this.conWidth ) {
            throw new Error("Element must be wider than it\'s container.");
        }
        this.lft = parseInt(adg.GetStyle(this.theObj,'left'),10);
        this.lft = isNaN(this.lft) ? 0 : this.lft;   // IE/Chrome return 'auto'
        this.inc = ( obj.inc ) ? obj.inc : 1;       // pixels to move per interval
        this.gap = ( obj.duration ) ? (obj.duration / (this.objWidth - this.conWidth)) : 30;
        // ..defaults to 30ms intervals

        var that = this;    // preserve scope
        if ( obj.bLeft ) adg.AddEvent(adg.$(obj.bLeft),'click',function(e) {
            return that.MoveIt(true);   // true = move to left
        });
        if ( obj.bRight ) adg.AddEvent(adg.$(obj.bRight),'click',function(e) {
            return that.MoveIt(false);  // false = move to right
        });
        if ( obj.bToggle ) adg.AddEvent(adg.$(obj.bToggle),'click',function(e) {
            return that.ToggleMove();
        });
        return this;
    }
    Carousel.prototype = {
        constructor : Carousel,     // otherwise it inherits Object.prototype
        CancelMove : function () {
            clearTimeout(this.theTimer);
            this.Moving = false;     // -inc = left, +inc = right
        },
        MoveIt : function (blnLeft) {  // blnLeft : true = left, false = right
            var MoveToLeft = function (blnLeft) {          // called by MoveIt()
                if ( blnLeft && (this.lft + this.objWidth >= this.conWidth + this.inc) ) {
                    this.lft -= this.inc;
                }
                else if ( !blnLeft && (this.lft <= -this.inc) ) {
                    this.lft += this.inc;
                }
                else {
                    this.Moving = false;
                    return false;
                }
                this.theObj.style.left = this.lft + 'px';
                var that = this;    // preserve scope
                this.theTimer = setTimeout(function () {
                    MoveToLeft.call(that, blnLeft);
                }, that.gap);
                return true;
            };
            if ( this.Moving ) {
                this.CancelMove();
            } else {
                this.Moving = ( blnLeft ) ? -this.inc : this.inc;
                MoveToLeft.call(this,blnLeft);
            }
        },
        ToggleMove : function () {
            var ml = this.Moving;       // was it moving already?
            this.CancelMove();
            if ( this.lft ) {
                ( ml > 0 ) ? this.MoveIt(true) : this.MoveIt(false);
            } else {        // it's already furthest right..
                this.MoveIt(true);      // so move it left
            }
        }
    };