According to my OBDII manual, a code 171 indicates that the system is running lean. This is not necessarily from an air leak. It could be a faulty mass air flow meter, or could be something as simple as plugged injectors. My first step would be to put some injector cleaner in the fuel tank. My personal choice would be BG44K, although it is not carried in many parts stores. After that, I'd try to find a friend with the same car and temporarily swap MAF sensors with him to see if that cures the problem and moves it to his car. Finally, you can check for vacuum leaks by spraying starting fluid around your hoses and listening for an engine rpm change. The boot from the throttle body to the mass air flow sensor is the most likely culprit. Inspect it carefully.
Dr. Loot's Assistant
Wednesday, October 28th, 2009 AT 12:19 AM