Q: engine hesitates and knocks

Hello, thank you for writing in. Hesitation and knocking can come from several different components. The work you have done so far is perfect and allows us to focus on other systems. When it comes to hesitation the oxygen sensors come to mind. These will have significant affects on the engine and computer and how they drive the vehicle. However the knocking sound typically only occurs when the catalytic converter has failed, and we do not want to assume that yet. Start with the easier components that can cause these issues like the canister purge valve. This is a small part that you can unplug for a quick test. If the symptoms get better once the valve is unplugged, you will know the valve needs to be replaced. For more help diagnosing and repairing the issue, contact our service department.