kiwikev

Hi. 2002 5.4 125K Began idling rough, almost died, changed plugs. No better. Got codes 0171 and 0174. Intermittently runs fine. Real bad last 2 days. Wouldn't restart when warm [ cough,sputter,bucking,die out]. Read lots of posts and checked vac system [ no leak- elbow at back of intake good], cleaned MAF sensor and throttle body, got same codes again. Today I had to wait until totally cold and then restarted after 1 crank where it died. Injectors sound like they are working. So before I start spending on o2 sensors,,MAF, ignition coils etc randomly I wondered if anyone had a suggestion as to where I should start? Could it be bad cat converter? Any ideas would be appreciated.
Kev

Bronco302

Is your vehicle equiped with a cold air intake of any kind, I have found the oil from these filters tend to contaminate the maf sensor? If so I would recommend cleaning the maf with a maf sensor cleaner spray. If it has the stock air cleaner and your air filter has been maintained recently i would want to check your fuel pressure first, as this is something that can cause a lean on both banks. Have you ever replaced your fuel filter? If not it could just be a simple case of a clogged fuel filter. If your fuel pressure is ok i would probably want to try smoke testing for intake system leaks or if a smoke tester is not avaliable then spray brake clean on your vaccum lines and around the base of the intake manifold and if the rpm increases then that indicates a vaccum leak. If you have access to a scan tool you can monitor your o2 sensors or short term fuel trims when spraying brake clean to see if they spike when spraying certain areas.
I hope this helps.... Let me know what you find
Devin

JCR 56

It could be running lean because it's actually not getting enough fuel, instead of a vacuum leak causing the codes. I would check fuel pressure, needs 28lbs to start. I would replace filter first if it hasn't already been done. The pump itself could be on the way out.