I got a 2002 Ford Explorer V-6...Starts no problem. However, while idling...or at stop signs or red lights the truck lunges and runs rough. It has died a few times. It idles Erratically to the point where it dies on occasion. But starts back up. Tonight while riding with the family the engine light popped on to say hi! .....I ran the code and it came up with a P0171. I cross referenced and it says its a system to lean bank #1. What should I start checking....any advice....direction....Appreciate any....

 

Sounds like you have a vacuum leak. The plastic tee fitting for the PCV valve and the lower intake manifold gaskets are common problems. The IAC valve can cause idle problems too but many people unnecessarily replaced them simply because it is an easier place to start than finding a vacuum leak. If you suspect the IAC valve, try cleaning it first. If cleaning does not substantially improve the idle, replacement probably will not solve the problem and would be a waste of money. The TPS sensor is another common shot in the dark, but don’t waste your money. Like the IAC people often replace the TPS because it is easy and they don’t understand what it affects.

Does it run rough only at idle or at higher RPM too?

 

Only at idle i will check the tee fitting right now cause i am out back changing the oxygen sensor on the #1 side upstream because auto zone says that is the cause

 

While there is a possibility the 02 sensor is the problem, it is unlikely. Remember the 02 sensor’s function is to tell the computer when the engine is lean or rich. Then if the lean or rich condition is within the range that can be corrected by the system it will make the adjustment. It does this constantly while you drive. When the condition exceeds the systems ability to correct it, a DTC code is set and the CEL/MIL light turns on. Most likely, the 02 sensor is working correctly and is just doing its job. Autozone employees generally have good intentions, but they are paid to sell parts and are rarely trained repair techs. I hope they were right and it fixes the problem but I’ll bet it doesn’t.

 

hey no fix what do u know $60 down the pipe i hear something like a vacum leak i did try to pin point with a stethascope but no luck i cant find the tee from the pcv to the intake all i see is 1 big 90* fitting that comes off the intake into 2 or 3 smaller lines looks like that is all 1 piece and with the stethascope i hear no noise......i got a vacuum gauge on the fuel pulsation damper and i got 18.50 but when i rev the gas the pressure starts to go down when i let off it goes back up....

 

Got a new code po174 with the po171 so i am going to check the fuel pressure and see if i need a fuel pump.......... Not sure how much pressure i should have party at my garage

 

As a general rule, a lean code means that the O2 sensor is working, but despite the computers best efforts, it is unable to compensate for the issue. Be aware, that running lean is not the only issue that can cause a code. If you are running rich or misfiring, the code can be set too, because the oxygen in the cylinder is not consumed in a burn. Just something to ponder. Most likely it indicates a plugged or faulty injector. Bad plugs and wires can do it as well.

 

AutoZone will be happy to sell you the fuel pump, a fuel filter, and the tool to disconnect the fuel line. They probably have the fuel injectors too. After you install everything, you probably will still have the code because you will still have the vacuum leak…

Because it takes more fuel to drive than it does to idle, low fuel pressure or injector problems usually create drivability problems (typically hesitation, bucking or surging) long before you would notice anything at idle.

Vacuum leaks, however, are masked by higher RPM because of the increased airflow. The engine runs smoother as the leak becomes a much smaller percentage of the total air/fuel ratio, but the computer can still sense the potentially damaging lean condition. That is what your computer said you have. Misfire and a rich condition have their own specific Diagnostic Trouble Codes. The computer can tell the difference.

I know it is no fun chasing a vacuum leak, but it is still the most likely cause of a lean condition.

 

a bad mass air flow sensor is more than likely the problem. i have changed many of them. doing the same thing that you are saying. but you have to have a scanner to be able to test it.

 

I agree that the MAF sensor is a possibility. Sometimes cleaning is all they need. Snap-on sent their customers an e-mail with instructions. Use denatured alcohol and a cotton swab to clean the resistive wire in the sensor.