Check Engine Light

[Em91]

Hello everybody I just got a code#25 while running a diagnostic on my car. The book says that this is a 25 Air–Fuel Ratio Lean Malfunction . Two weeks ago I had to put in an air flow meter that I bought at the junk yard. Does anybody think that it could be the same problem. Thanks. Oh I have a 91 ls400.

[ModMan]

Could be O2 sensors.

[92Lex]

It could be your O2 sensor(s) like modman said....but yeah, it might be that MAF sensor you bought at the junk yard. Test the MAF sensor before you replace it with another one....you tested your old sensor right?

[Em91]

Hey 92 Lex my car was running fine for 3 weeks. How would you test the air flow meter. I dont know how to test it. I checked online to see how to test it but it shows that you need special tools. Do you know a way to test it. I was also checking online and I read that it could be an exaust leak or a vacume leak or several other things.

[92Lex]

You have to use a quality digital storage oscilloscope....hook the red wire to sensor signal and black wire to the signal ground...check to make sure the frequency increases when the volume of air entering the induction system increases...there's actually more to it then what I've explained but if you buy or rent a oscilloscope I'll be more than happy to walk you through it.

Yup, it could be an exhaust or vacuum leak before the O2 sensors...but you should check all sensors first before looking for the leak (unless it's an obvious leak).