2000 Mazda 626 P0171

Beside going over the things that could have been dislodged when replacing valve covers, see the trouble code section this forum for causes/solutions.

Hi Jose, Sorry about your woes and shortness on answers, but if you go back to this page: http://www.obd-codes.com/trouble_codes/ near top of page there is a link to a good article on fuel trims. Go there and read it in full; it may help you understand it a little about fuel trims because there is a lot more to know. The writer does a good job of explaining it, but you really need to know more to fully understand what is going on. That is part of what the previous person was getting at for you to read. On the other thing about changing your valve cover gasket, he is right. You need to check for vacuum leaks and check for other places of possible vacuum leaks, specific to bank 1. The P0171 is a bank 1 (bank nearest firewall) lean trouble code, primarily caused by the o2 sensor reporting too much o2 in the exhaust, that will then cause computer to compensate by increasing the pulse signal to the injectors on that bank. In your case, you just changed the valve cover gasket, I suspect that gasket r&r was on bank 1. I hope you followed the proper tightening and torque sequence. Finally, you might want to pick up a good OBDII scanner that is able to give you live feed info that includes Short term fuel trim (STFT) and Long term fuel trim (LTFT) and a lot more data. If you go to Harbor freight you can pick up a good one for the cost of a diagnostics charge at most good repair shops (somewhere between $99- $135). Here is a link to one you may want to consider: http://www.harborfreight.com/can-obd-ii ... 60794.html I hope this helps point you to resolve your fuel trim problem. Good luck