Ticking Valves at 50+ MPH while motor is unloaded

Hey Guys, I have a 2002 Toyota Corolla CE with 160,000 miles on the odometer. While driving at highway speeds (50+ mph), if I let off the gas ever-so-slightly, an audible ticking (like the sound of a sewing machine) begins. It immediately goes away as soon as the motor begins to decelerate or accelerate again. It ticks the loudest while the motor is directly in between accelerating and decelerating, while I am trying to maintain the speed I am traveling at. The sound started 6 months ago and was almost unnoticeable, but has gotten steadily louder the more I drive it. From what I have already researched, I believe it might the valve lifters needing to be changed, but wanted to get a second opinion. Hope someone can help me out! Thanks a bunch! - Nick

Have you checked or had checked the valve clearances? It is pretty straightforward to check but a real chore to change the clearances as the lifters have to be changed to readjust the clearances. Think removing the timing chain gears; lifting off the cams; measuring the offending lifters; purchasing the new lifters; reinstalling everything; and checking the work. You would also be looking at the tension on the cam chain as well as the serpentine belt tension.

The other area of concern for a engine at this mileage is piston slap that would show up at low combustion heat conditions.

Otherwise, no help here.

Just to take combustion issues out of the equation, try a tank of 93 octane gas.