When the engine idle speed will not remain constant, check for the following, as necessary:
- A faulty fuel pump.
- A leaky Exhaust Gas Recirculation (EGR) valve.
- A blown head gasket.
- A worn camshaft.
- Worn timing gears, chain or sprockets.
- Leaking intake manifold-to-engine gasket.
- A blocked Positive Crankcase Ventilation (PCV) valve.
- Overheating of the cooling system.
- Fault with the computerized engine control system.