janettis

My 98 4Runner is throwing a lean code. I brought it to the shop and they replaced the air filter, fuel filter, and clean the mass airflow sensor. A few days later the code came back. They told me that I probably needed a new MAF sensor. However I pulled it out and re-cleaned it, and put it in my 97 4Runner and drove the '97 for a few weeks including over mountain passes and never got a code. I put it back in the 98 runner and after driving a few days got the code again.. It is not running sluggish at all and is idling normally so I don't suspect the fuel pump. What else could cause this? I appreciate your feedback . I also need valve cover gaskets replaced. Could this cause that code?

Co_94_PU

iTrader: (-1)

The lean code indicates the ECU has exceeded its ability to adjust the fuel trim. This could be inadequate fuel supply (clogged injectors, loose ground wires). Air entering the system the ECU doesn't see, (cracked or leaking air hoses, bad gaskets). Faulty sensor readings, (failing o2, coolant temp, air meter)

You will actually tend to gain power when running lean right up till you melt a valve or piston.

PS your auto shop sucks, find a mechanic that will diagnose the system not a "technician" who just throws parts at a problem.. The factory manual provides exact steps to not only test the system but procedures to verify the issue has been fixed. This code uses what's called "two trip detection", which is why it took a day to come back, they did not follow the verification steps.

janettis

Great information! Thank you so much!