Spark plug tube seals fail, causing the tubes to fill with engine oil and the engine to misfire. As a result, the engine may run poorly and fuel economy can suffer.
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Most reported 1999 Plymouth Neon problems
There have been reports of premature head gasket failure; an updated gasket design is available to correct this problem.
If a Check Engine Light illuminates indicating leak detection pump (LDP) failure, the cause is often pinched or disconnected vacuum lines to the pump. Vacuum lines should be inspected before replacing the leak detection pump. Contamination (carbon or debris) in the pump can cause failure and any hoses should be cleared before a new pump is installed.