I'm having a prob with my IS300. I'm getting a maf code(P0171) and a lean code(P0174). At first when i would take my car out for a drive I'd run into a little bit of a fuel hesitation when I would step on the gas up a hill and never really thought about it. But now i get it really bad in 1st and 2nd gear once in a while. So this is what i have done after all this has happened.

1. Went looking for a vacuum leak but cant seem to find one(Not saying there isn't one just cant find it)

2. Cleaned maf off with maf cleaner stuff and let dry for more then 20 min and also cleaned airfilter.

3. I seen a gap in one of the seals on my throtle body and RTV'ed it and the hesitation seem to get a little better but not going away.

4. decided to run injector cleaner throgh the fuel(Some stuff at the gas station then did seafoam on next fill up)

5. Pulled break booster hose off and the car almost instantly dies not sure if thats just how newer cars are and ran seafoam throgh vacuum lines and it seemed to run awsome for a bit but then i got the check engine light again. Also when i started the car up again after putting seafoam in the vacuum lines i did notice that there was a little bit of white smoke coming from somewere under the intake manifold on the firewall side.

if all of this is confusing im sorry lol and also yes i know that there are post about this all over goggle but i can seem to find any that are helpful .... lol. Also forgot to put this up there i cleaned the filter be for the car really started to act up and used a recharge oil filter kit on it and i think the filter i have is a dry filter cause it just would not run very well lol stupid mistake lol didn't know injen made dry filters also lol. so any help would be most appreciated

 

have you replaced your mass air flow sensor?

 

Do you have access to a scantool that can read airflow count and fuel trims? That would be helpful in diagnosing your problem...

Best guess is the airflow sensor is defective, though they usually don't go bad on our cars...

To continue looking for a vacuum leak, get a can of starting fluid and spray it near anything that might be suspicious for a leak... engine rpm raises, you have found the culprit... intakes are pretty straight forward on our cars however, so it is unlikely, but there are quite a few vacuum lines and a few capped off places too...