mgex

Hello All,
I have a 97 3.4L 4Runner with a P0171 lean code that popped up just after I changed the valve cover gaskets and the PCV valve and grommet. I’ve reset it several times but it keeps coming up after about 3 drive cycles and always when I’m idling at a stop light. Engine performance and idling feels normal. I figured I just forgot a vacuum connection but I have checked all connections. After reading all the other P0171 threads around here I can’t see how I could have the typical culprits – MAF, O2 sensor, or fuel injector malfunctions – since these were all operating correctly before the valve cover change.
I even broke down and took it to a dealer for diagnosis (and to make sure I wasn’t missing something obvious) and they said everything looked good and the computer system showed all the sensors were operating correctly. The next step they recommended was bench testing the injectors but, again, I can’t see how these would have gone bad if they were not triggering a code before.
I’m thinking about trying a new PCV valve/grommet just to make sure there is no problem with those relatively cheap and easy parts. Sound reasonable? Any advice is greatly appreciated!
Thanks

Smokey

http://www.obd-codes.com/p0171

....A code P0171 may mean that one or more of the following has happened:

* The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
* There could be a vacuum leak downstream of the MAF sensor.


On a side note, I had this code show up right before my front O2 sensor failed. After cleaning the MAF, the code went away for about a month before the O2 sensor failed (different code that would not clear). I would take little carb cleaner and spray it on your vacuum lines and see if the engine bogs down.

Good luck!

nick-m

This code popped up on me after after a co-worker cleaned out my MAF with an air blow gun. Don't ask. I got some CRC electrical contact cleaner - problem solved. Cleared the code and it went away; so it could very well be a coincidence with the timing. Try cleaning the MAF before the dealer tries to rip you! I work at a dealership, I know ;-)

Homer666

Just echoing the above comments. I replaced my O2 sensors a couple of months ago when the dreaded 171 code popped up. That seemed to fix the problem for a few weeks (with a nice increase in gas mileage). However, after a trip over the Rockies to Langley, the dang code kept popping up. I cleaned the MAF and while the vehicle seemed to run better, the code came back a few days later. I ended up getting getting a new MAF from the local Toyota dealership and whoila!! No more codes and the gas mileage is not half-bad (450 km per tank going through the mountains - about 15.5 mpg per us gallon - hey....you should have seen it before the new O2 and MAF sensors LOL).

Good luck;

James

mgex

Thanks, everyone, for the advice. I should have mentioned - I did clean the MAF with electrical contact cleaner after the code came up with no luck. I do have 134K miles on my original O2s so I guess they are due anyway.

Anyone ever had an issue with the fuel injector gaskets breaking their seals? To get the drivers side valve cover off I did quite a bit of wrestling with the wiring harness that connects to the injectors.

One other thing - when I did the gaskets I also did the spark plug seals since a couple were leaking and one spark plug tube had about 1/4" of oil in it. I cleaned out the oil but could this have caused some issue? I'm not getting any misfire codes.

Thanks again

jeremy9allen

I would either carefully (watch out for ignition components) spray down your intake and vacuum lines with carb cleaner and check for a leak OR take it to a shop with a smoke detector that can check for leaks.

If bank 1 is the gasket you replaced, I would think it could be a vacuum leak. They can be very tricky to find and sometimes a smoke machine is the only way.

You did tighten down every clamp after the MAF sensor right? Any air leak after the MAF will give a lean code(s) because the MAF has already told the PCM the amount of air it is getting and does not know about any air getting to the motor after the sensor.

Good Luck