96 Mazda B2300 Idle Issues with Codes P171 and P301 After New Engine Installation
I recently installed a new engine along with all essential components including spark plugs, wires, sensors, and air filters. The vehicle now has only 500 miles on the odometer. Despite driving smoothly, I'm consistently receiving diagnostic trouble codes P171 and P301. The idle behavior is erratic—either running at a high RPM between 2500-3000 or dropping to dangerously low levels around 500-750 RPM, nearly stalling. Given the symptoms, I suspect a vacuum leak, though my experience with engine diagnostics is limited. Are there any reliable troubleshooting steps or common causes for this issue in a 1996 Mazda B2300? Any advice would be greatly appreciated.
Since you recently had a new engine installed and the trouble codes appeared afterward, it's important to revisit the shop where the work was done. If the codes weren't present before installation, they may indicate an issue with the new engine or its components—such as faulty sensors, improper vacuum lines, or misalignment in the intake system. Requesting a full diagnostic review from the mechanic could help identify whether the problem stems from installation or part quality.