Check engine light comes on for about 3-5 seconds then turns off. Doesn't happen all the time. I've changed the PCV valve recently and the O2 sensor about 6-8 months ago.

Hi there:
DTC P0171 - System to lean Bank 1

You might just have an air or a vacuum leak causing this code. This is pretty common. Be sure to check for vacuum leak such as hoses/lines leaking vacuum, intake manifold gaskets as well as the pcv hose behind the throttle body. I would check the PCV line from the passenger valve cover to the rear of the intake manifold. That line will collapse over time due to oil and age. It will create a vacuum leak. With the engine at idle, move the vacuum and PCV line and see if the idle changes and listen for a vacuum swushing sound. Both 02 sensors will not cause both of these codes.

Hope this helps.

Find out if Midas use a genuine sensor or an after market unit. A cpu is set to read the parameters of a genuine unit and after market units while they work have the parameters set so that the cpu sees them as faulty and will put the engine light on.. Suggest you take it to a dealer for a correct fault reading and diognosis of the problem.

O2 Sensors only reads Oxygen Content in Exhaust
Converter,so forget that persons advice in the future

The O2 Sensor info is for adjusting fuel trim or injector
pulse timing,not your problem

You change front upstream O2 sensors at 100,000
miles, as preventative maintenance

Check Fuel Pressure at motor & pump maybe failing
as well,doesn't hold pressure thus takes too long to start

Clean the Air Idle Valve on throttle body & it won't shut off
at stops

Check all your vacuum hoses especially at the PCV coming off the valve cover it is often over looked. The PCV fits loose either put a new bushing in the cover or add some black tape to the PCV at least until you figure out that might be the issue. Also your timing should be at TDC or 2 degrees plus or minus. Contrary to popular belief You can use a timing light you can see the timing mark know about where it is and line up the fly wheel mark accordingly.

Try unhooking your battery. It should reset the light. If that doesn't work it could be the relay again. I have had that happen to me with my 2001 Expedition. Was told it was caused by me giving someone a jump and it caused the service engine soon come on.

Fords require the fault to be present for two ignition cycles before it will turn on the check engine light. Unplug all the O2 sensors and then replace the fuse. If it stillbloys than you know the problem is in the vehicle harness. If it doesn't blow plug the O2 sensors in one at a time until the fuse blows. Replace that sensor. Posting the actual code or codes that are present would also be a good idea. Let me know if you have any questions and I'll do my best to answer them. Thank you for using FixYa.com!

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Check engine light is blinking a code, a auto parts store can read codes for you most the time its free, sound like maybe a few diff things, the EGR valve maybe stuck open or shut, or a O2 sensor, or Mass Air Flow Sensor, they do make a mass air flow cleaner thats the only thing you can use on it, the mass air sensor is just after your air filter on the tube that runs to the motor, the O2 sensors are on the pipes before and after the converter. Egr vents the non burnt gas back in your motor to re burn it the pipe coming off the manifold back up to the top of motor should see a egr would have a round diaphram looking thing on it. start with the codes being read at auto zone or O''rillys. i know on that that Rodeo you have to change the PCV valve about every 15,000 mi it vents the air out of the motor, run about $3, worst case senario it jumped time,

did you replace your pcv valve? you should also change your air filter. that shoudl do it. be aware , sometimes it takes a few DIFFERENT types of engine conditions to reset the computer. sometimes the engine has to reach a certaain temp and maintain (at some interval) , then be turned off for a certain duration of time to reset.

I would check the air filter, pcv valve (take it off and shake it), spark plugs and wires to see if it's just time to change em'.

Hi, the egg smell is an early sign of bad valve timing and bad seals as well. the engine light normally, will signal a change for a specific sensor like a O2 sensor or egr valve or pcv malfunction.


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