NOx emissions are normally due to defective EGR valves and/or systems. High compression, high engine temperatures, and/or vacuum leaks may cause high NOx also. If after all emissions systems are inspected and no faults found, consideration should be given to the CAT.
Having fixed the PCV problem might allow NOx to return to normal values however this can not be guaranteed until a second smog test is obtained with the PCV hose connected. NOx normally being caused due to defective EGR systems, we recommend inspecting the EGR system prior to a second smog check (assuming your Plymouth Acclaim is equipped with one). According the the Mitchell Emissions Application Guide, the automatic transmission version of your vehicle is equipped with an EGR valve and the standard transmission version is not.
Your Plymouth's EGR valve should be inspected to ensure its proper operation. A working EGR valve should be able to open its passage using manifold vacuum. Manifold vacuum is created during the engine's intake cycle. The high demand for air during this cycle creates a vacuum within the engine's intake manifold.
EGR systems are prone to collecting carbon build-up. Since the EGR valve pulls exhaust gasses from your exhaust and introduces them back into your engine's intake air over time it will become clogged or stuck open/closed from the carbon deposits. It is possible to clean the EGR valve if you remove it from your vehicle and either spray it out with a parts cleaner. Also ensure the EGR passages on the intake and exhaust manifolds are clean.
