Periodically, the Positive Crankcase Ventilation (PCV) valve is to be examined whether it is clogged or not. It is fitted to the intake manifold (below the carburetor) on trucks as early as 1984, and in the valve cover in 1986-89 trucks, to which it is connected via a vacuum hose. To check the PCV valve, take it out of its mount and shake it, there should be a clear rattle sound and otherwise the valve must be changed. To be removed and installed on trucks up to 1984, one must first remove the air cleaner, then loosen the hose connection to the PCV valve, and finally remove the valve in intake manifold fitting. Install the valve are again in the fitting and reconnect the hose, then attach the hose on the air cleaner and fit the air filter, ensure that correct clamps or cracks in the PCV lines are not loose and replace those that are broken. In the 1986-89 models, you just have to pull the PCV valve out of the grommet in the valve cover, take off the hose clamp then from the hose and then install the new valve and clamp. In case the engine has a low than normal gas mileage, and it is also poor in idle, then the PCV valve is probably backed-up and it has to be removed and replaced.