Valves and lifters function as part of a vehicle's valve system. Valves open and close, allowing compression for the power stroke and the release of exhaust gases. Valve stems can stick either permanently or sporadically, due to heavy varnish on the valve stem or weak return springs. Lifters control the valve movement up and down. Without doing major repairs to the engine, a vehicle owner can try a few simple mechanical procedures, or he or she can a use a specific additive to cleanse and lubricate the parts.
Set the vehicle in park and engage the emergency brake. Start the engine and raise the hood. Allow the engine to reach operating temperature. Use the stethoscope to listen for any clicking or clacking noises coming from the top of the valve cover, which looks like a long rectangular box (or boxes) on the top of the engine. Sticky valve and lifters noise, which will sound like a muffled clicking or clacking, will come from this area. A valve that becomes frozen, or only moves up and down slightly, might cause an engine miss that sounds like a popping noise, and you might notice a hesitation as the car tries to move forward.
Shut the engine off. Check the level of the engine oil, and fill the crankcase with the proper level of oil as marked on the dip stick scale, which will be shown by a line that has the word "hot" next to it. A very low level will cause all of the lifters to click, causing a machine-gun like clicking that comes from both the front and rear of the engine. See if the noise persists after filling to the proper limit.
Check the dip stick for a too high reading of the oil level. Any oil mark up past the hot fill mark can allow air bubbles into the system. If the level appears too high, drain the proper amount of oil from the crankcase until it reaches the appropriate level on the dip stick.
Add a full can of oil additive, like Marvel Mystery oil, to the crankcase. This fine machine oil will penetrate into deep into the valve and lifter areas. Run the vehicle on the highway for a few hours, using some hard acceleration--don't lug the engine. Upon arriving home, wait for the engine to cool and then change the oil and filter. Any minor sticking valve or hydraulic lifter should disappear after this treatment.
Make sure the engine has been turned off and remains cool. Remove the valve cover (or covers) with the appropriate socket. Look at the valve springs, which are very thick springs about the size of a D-cell battery. Small retainer clips sit on the top of each valve to hold it in place--make sure all of the small clips sit in their proper position. Spray penetrating oil inside the spring, where the valve stem sits. The valve stem will be shiny and have the diameter size of a pencil. Let the penetrating oil soak for several minutes.
Gently tap on the top of the valve springs with a small hammer. Tapping the tops of the valve springs with the hammer will sometimes free up the valve stem shaft so that it can move properly. Replace the valve covers and listen for any clicking or clacking noises.
Obey speed limits when using the hard acceleration technique.