pinoyballa

my 1999 160,000 miles rx300 threw the infamous p0171 cel code. i did my search and a lot of threads came up about replacing the af sensor and cleaning the maf sensor. I just dont want to replace it and find out it was something else so I'm thinking about bringing it to the dealer to diagnose it and depending on what it is, do it myself if i can.

is it okay to continue to drive with this cel or should i keep it in the garage until i can get it serviced?

just a fyi: last month i replaced the spark plugs with the oem denso ones, replaced the coolant, transmission, tranfer case and rear differential fluids.

code58

Take a look here and see if any of this helps you out. http://www.obd-codes.com/p0171

Leines

battled twice... so far looks like both times it came up MAF sensor.... you can try the cleaning first there is a set by step thread on here on how to do it.... first time the toyota dealer just cleaned mine..code went away i put 25,000 kms on the truck without the code coming back...

GS4_Fiend

iTrader: (22)

P0171 - Bank 1 Too Lean.

MAF sensor would cause both banks to go lean.
I would check for and vacuum leaks first. The best way to detect a vacuum leak is with a smoke machine. Usually the intake manifold gasket leaks and they are located on bank 1. You can easily identify by doing a smoke test.
If no vacuum leaks, the only thing left would be a bad A/F sensor or bad wire integrity to the A/F sensor.

artbuc

Yes, it would cause both banks to go lean but for some reason, in almost every case, the DTC is P0171 w/o P0174. I've dealt with it personally on three different 1MZFE engines and have read many, many posts of dirty MAF sensors causing P0171. Start by cleaning your MAF. If you have never cleaned it, it will be pretty dirty at your mileage. Make sure you clean the wires and not just the IAT sensor bulb.

Did you disconnect any vac lines when you did your recent maintenance work?

PS I just had an experience where I installed my throttle body gasket 90 degrees off and had a big vacuum leak. My code was P0171 - no P0174.

pinoyballa

I cleaned my maf sensor a couple days ago and haven't had the Cel come on yet. It's been 150+ mile since I cleaned it.

Im trying to narrow what caused the cel:
1. I replaced my air filter a month ago. Would the increase in air throw the code?
2. Dirty maf sensor
3. When I went to clean the maf sensor, The back end of the maf sensor wasn't screwed in all the way.

Any ideas which of the 3 could have caused it?

Leines

Im not an expert by any means, but ive read on these forums that a new air filter if its aftermarket has sometimes been pointed to as clogging the MAF, as the aftermarket has small particles that fall off or something the toyota doesnt, the MAF been dirty is known to cause this issue at least thats what toyota said when i had that CEL.
Id think it could have been caused by any one of the three... but #2 is common to all even if it was just not screwed in all the way...LOL

LA4Mead

When P0171 with no other codes is thrown, does that usually mean it's time to clean the MAFS again?

It doesn't seem like it's been that long since the last cleaning... Just asking.

Thanks!

GS4_Fiend

iTrader: (22)

Could be a vacuum leak on bank 1, defective pcv, or bad a/f ratio sensor. But clean the MAF sensor anyways.