Cam Phasers - They adjust the cam timing by oil pressure, once they start to get wore at about 40,000 miles, when you drop to an idol the oil pressure drop causes them to not hold time and hence the rough idle. Changing oil to a 5-30 then a 10-40 will make the ticking go away and prolong a change of the cam phasers but only prolongs the need to change them. It is a to day job, I ordered the phasers, cam positioners and timeing chain kit from rockauto $650.
