jwh34761

So I'm having an issue with my truck. I can start the truck and go drive or just let it idle for a period of time, then turn it off and back on and it really hesitates to stay running. The RPM will stay below 1000 and fluctuates from near 0 to 1000. Its a 50/50 chance if it corrects itself and runs normal or stalls out. if it stalls out its even a less chance that it will start again. If i let it sit for around 45minutes to an hour it starts up fine no issue. it is throwing a P0171/p0174 code. I have replaced the coil pack,spark plugs,MAF sensor,O2 sensors,EGR Valve,EGR valve pressure sensor, EGR vacuum solenoid, and its been to the shop to fix all of the vacuum leaks. I'm running out of ideas on what it could be, i plan on possibly replacing the fuel pump, the pump relay, and fuel filter. tonight is when all the EGR parts and spark plugs were replaced, and I'm not sure if its been doing it the whole time or not but after i put the new parts in tonight i took it for a test drive which felt like it had improved in some way but after returning home and letting it sit for 10 minutes, i tried to restart it but this time all the lights and power were flickering(its dark outside so it was more noticeable). it did stay running but threw the same two codes as soon as it started. the power flickering may be a total different issue as my battery may be going bad, but i'm at a loss and would appreciate any input given.

cainmin

Get a fuel pressure tester and check for propper fuel pressure. I beleive its about 40 PSI key on engine off, it sounds like your getting exsessive amounts of fuel to the injectors... may be time for new hardware on your injectors (o-rings and plasitc caps).. also theres an dpfe sensor right above the alternator has 2 small hoses going in and a CPU plug of sorts... this may help the problem but i cant promise its directly linked to the issue... those are 2 cheap fixes but the injector hardware is a pretty big job if youve never done it before.

RCButler

Could also be an issue with the throttle position sensor or pcv issue.
I had a hole in my pcv hose that created similar issues as you describe.

https://m.youtube.com/watch?v=3C9U7h3-WJk

http://easyautodiagnostics.com/ford/4.2L/throttle-position-sensor-tests-1

jwh34761

I have replaced the dpfe(egr valve pressure sensor) and the pcv and all the vacuum is fixed, truck was at the shop for 3 days. Ran fine for about another 3 days before problems started again. I just replaced the fuel filter this morning and I am currently replacing the down stream o2 sensors now.. I plan on doing the fuel pump soon and will most likely do the injectors now too. I have literally gone through just about all the troubleshooting for those codes beside the fuel system. I'm just about baffled and ready to take it back to the shop. I'm just trying to do what I can for less money first.

OTG02

It could be the isolator bolts. I had those codes. I replaced the isolator bolts and the upper plenum gasket and it went away and has not come back on in over 4 years. As for the flickering I have no clue.

jwh34761

I believe the flickering was from battery corrosion which I cleaned up today..