AutoMaticI

I have a P0171 code. Replaced the Bank 1 sensor towards the firewall and the one closest to the fan just 6 months ago. I have a diagnostic tool. I saw on youtube that longthrift should be less than 10%. Diagnostic tool says longthrift is about 20% after replacing the firewall sensor. The car runs pretty good. If the check light wasn't on I might not notice there's an issue. My diagnostic tool is a fairly expensive one and with some guidance it probably could help me. Can anyone please help? Need to go meet the new grand baby in St Louis in next day or two.

nsghtbrwry

Well, if the sensors are new (and hopefully good...cheap Chinese sensors are often crap, nothing like a new Denso/Toyota sensor), I'd clean the MAF (make sure to use specific MAF sensor cleaner, these things are fragile) and check for a vacuum leak. Listen for hissing, check for torn hoses. The "elephant nose" hoses from the air intake box to the throttle body often get brittle and rip with age, that's a place to start.

AutoMaticI

Front bank is bosche - engine wall sensor is Denso
It actually runs pretty smoothly. I checked the hoses and all seem to be good.
I don't hear any hissing noise either.
MAF took off I used non chlorinated parts cleaner- generic kind. Do you think that could have hurt it? Should I try to go buy sensor clearner and redo>?

nsghtbrwry

I don't know specifically if non-chlorinated parts cleaner, which is canned acetone, could have hurt it; but I've always heard people warning never to use anything but MAF sensor cleaner on them. I do know people that used throttle body/carb cleaner and destroyed their MAFs.

I guess you could try, but if the sensor is damaged you might need to get another (I'll recommend the Denso unit). I hope the Bosch sensor isn't the problem, those tend to be vastly inferior to NGK in specific applications unless they're, well, reboxed NGKs (especially Toyota/Honda applications. Trust me, I used to be an emissions engineer and they were both my suppliers).

AutoMaticI

Well, I read the 1mzfe manual and it said to test the MAF. See attached. Now, I turned the OHM tester to 20k, and I tested as the attached shows. My reading showed only .75. I ordered a Cardone remanufactured MAF that I'll pick up tomorrow to see if that fixes it. The bank 1 sensor towards the radiator is a bosche but it should still be under warranty at carid. I'm not sure I'm setting the ohm tester to the correct position though. I intend on testing the MAF the same way I tested mine at the Oriley's store tomorrow before I even take it out the store.

AutoMaticI

OK. I've replaced both sensors -the one by the radiator and by the firewall. I used Denso 234-4622 for both since I was told by the lexus dealership they are the same. I've replaced the MAF- it's a cardone. Now- I've used the OBII tool and the long thrift is way high especially when I rev up the engine. Total thrift is about 35 or 40 with the long being about 29 and short about 9.xx. Can anyone help with what my next step should be? Light came back on P0171

nsghtbrwry

Not "thrift," LTFT and STFT - Long-Term Fuel Trim, and Short-Term Fuel Trim.

Those numbers are really high - either you have a bad vacuum leak or the MAF is bad. Rare occurrence if everything else checks out: ECM is bad.

I had a similar problem on a '99 ES: LTFT was 25.8, which couldn't be right...it wasn't throwing a lean code, though. I probably could've cleaned the MAF, but I replaced it with a brand-new Denso and everything went normal (LTFT at 0.9).

I would first do a thorough inspection for vacuum leaks. Read up/watch videos on using carb cleaner or propane to find vacuum leaks. If everything checks out, thoroughly test the reman MAF and post your results back here. This link might help you with using the multimeter: http://forums.mikeholt.com/showthread.php?t=133722

AutoMaticI

I did what nsghtbrwry said and that was to spray carb cleaner around on hoses and I sprayed it around the throttle body gasket and egr valve gasket. I noticed that when spraying it where EGR valve gasket is and the car almost died. I also notice a change in the engine when spraying around where the throttle body gasket goes on. I ran to Autozone and got a new gasket, and took off throttle body and EGR. I lightly used sand paper on both sides of where the throttle body gasket goes and both the top part of egr as well as the lower part. Then I used toyota sealant on both sides of everywhere. I drove it a half hour yesterday and this morning it didn't turn on either. OBII scan tool shows LTFT at 14 and STFT at 1 or 2 after driving for the half hour which is way better than the 39 total that I was getting before the fix. I HOPE it stays off. Thanks alot nsghtbrwry for the how to find vaccum leaks! I was about to take it to the shop!