Q: i have 3 code on my car P0431, P0174, P0305

Noise in exhaust systems occurs due to leaks as well as internal failure of the baffles in the muffler or resonator. So, just because there are no leaks, doesn’t mean the exhaust system will be noise free. An [engine/exhaust noise diagnostic(https://www.yourmechanic.com/services/noise-from-engine-or-exhaust-inspection) could be performed. The motor mount can be visually inspected and tested; they should have been able to give you a conclusive answer as to the condition of the motor mounts. With regard to Diagnostic Trouble Code P0174, if there is tape applied to repair the rubber air intake boot, then the boot does have to be replaced as part of any diagnostic for Code P0174 simply because leaks at an intake boot are a known cause of Code P0174. Once an obvious fault is found in a diagnostic, such has to be repaired in order to complete the rest of the diagnostic and indeed such repair may conclude the diagnostic because the torn boot might the faulty component that caused the Code to set. Once the rubber air intake boot is replaced, if Code P0174 recurs, additional possibilities have to be considered such as: other air leaks (other than the boot) after the mass air flow (MAF) sensor including the intake manifold gasket, a dirty or faulty mass air flow sensor, a faulty oxygen sensor, incorrect fuel pressure, leaking positive crankcase ventilation (PCV) valve, clogged exhaust gas recirculation (EGR) port, and leaking brake booster.

Trouble code P0305 relates to cylinder No. 5. The coil is only one possible fault that might set this code. The following additional components have to be considered or tested: the spark plug; spark plug wire or plug boot which could be leaking to ground; valve cover could be leaking oil into the spark plug holes and shorting the spark plug to ground; and power supply to the ignition coil. Trouble Code P0431 typically sets if there is an exhaust leak, the catalytic converter is not working and/or an oxygen sensor is failing or has failed. What I recommend you do is get a check engine light diagnostic. At the conclusion of that, the Mechanic will let you know specifically which components are faulty, thus causing these codes to be set, and itemize for you the required repairs and the cost. Please let us know if you have additional questions or concerns.