Ford Repair Questions? Ask a Mechanic for Answers ASAP
Welcome, I'm Chris (aka Moose) I'm an independent contractor here at Just Answer.
Code 538 can mean the engine rpm did not increase during the KOER test, there was throttle application during the test. This code will not cause the smog issues. Have you cleaned the intake and valves using sea foam fogging the intake through a vacuum line? Have you checked the compression and fuel pressure? Have you changed the air filter and fuel filter?
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