Why does my car still perform poorly after a full engine service?

Thursday July 2 2020


By Paul Kaganzi

Hello Paul, my Toyota Corolla 1998 model developed unstable performance after the two-month lockdown. I have serviced the engine oil, oil filter, spark plugs, air cleaner and fuel filter but the engine keeps surging and reducing power. Fuel consumption has increased, the engine idle is unstable and there are traces of oil in the throttle, air cleaner and engine top cover area have this new problem? Peter

Hello Peter, your Toyota may have a faulty Positive Crank case Ventilator valve also called the PCV. It may be necessary to inspect the PCV valve and confirm that it is not blocked.
The PCV valve is located above the engine valve cover and ventilates crank case blow by gases from the engine.
During combustion, the burning of fuel and air mixture releases blow by gases which can build harmful pressure in a car engine.

The PCV valve separates engine oil from these gases while releasing them into the air intake system where these gases are re-channeled as hot air to help the throttle unit regulate the ratio of fuel air mixture.

When a PCV valve fails or gets blocked, it tends to increase internal engine pressure which damages engine oil seals and gaskets and leads to engine oil leaks at the valve cover and in the air intake chamber or throttle unit.

A bad PCV will also cause a buildup of moisture in the engine which accelerates formation of harmful sludge (lumps of oil).

Poor fuel economy, erratic engine idling and occasionally engine stalling or failure to start will follow when a PCV valve fails or gets blocked and the hot air does not access the intake system to help stabilise engine running as well as regulate fuel-air ratio.


PCV valves should be checked or replaced after 100,000kms. Use of good quality engine oil blended with acid control and anti-sludge additives helps to protect the engine as well as prolong the service of its PCV valve.