I have a 2000 f150 lariat 5.4L 4x4 and when i start my truck up when it is usually below 40 my truck will idle around 300rpm and shake. It also makes popping noises in the exhaust. I am getting codes PO171 and 174 (running too lean in both banks) I have replaced my IAC, plugs, pcv valve, air temp sensor and MAF sensor and 02 sensors and nothing has changed. I have tried looking for for vacuum leaks using carb cleaner and starting fluid but i nothing has came up. I took it in to a mechanic and he suggested a bad intake manifold but i searched for a leak and found nothing. If you have any suggestions please let me now ASAP.

 

there are several things that can add to your problem, it is one of those things that hands on is really important.
plugged cats can do this, there is a tsb for bi-fuel with this problem.also check to see no one stuffed your exhaust with a potatoe or ???
one bad coil can do this, it shorts out the pcm from running normal.
bad fuel can do this, have you filled up somewhere other than your normal place, take a sample smell it. compare it with a known good sample.
low fuel pressure can do this, you need to check that you have at least 35psi.
internall automatic transmission problem can do this, does the oil smell burned?
Also software can do this, do you have a tuner, can you unplug it, if you do the damage can already be done.
ALSO THE WRONG WEIGHT OIL CAN DO THIS, IF YOU ARE RUNNING ANYTHING OVER 5W20 THEN WHAT CAN BE HAPPINING IS THE LIFTERS CANT BLEED SOON ENOUGH HOLDING THE VALVES OPEN, THIS PROBLEM USED TO BLOW THE OIL FILTERS OFF COP CARS WHEN THE 4.6 FIRST CAME OUT AND THEY WENT THRU THERE FIRST WINTER WITH THE WRONG OIL... (ALSO IF YOU HAVE REALLY OLD OIL IN THE CRANKCASE)
Good Luck

 

thanks for the response.

I forgot to mention i have replaced the catalytic converters, and tested the fuel pump which has 30-40 psi. I brought in to a mechanic and ran tests and it showed no misfires. Everything on the scanner showed that the vehicle was running normal but it definitely is not. I tried to look for leaks in hoses and the intake manifold but found none. Planning on doing a smoke test but not sure i will find anything. I was told that it could be the throttle position sensor? If you have anymore thoughts please let me know?
Thanks

 

Hey dont fall for the t.p. sensor trick causing this evil. on mostly any Ford if you disconnect the t.p. it will run and rev up, the reason is more than i wish to type here. However you can un plug it and try to rev the engine and see what happens, it could be shorted to vref power... another long story. IF this repair is getting out of your expertise you could go on craigs list and search for a Ford tech and work out a price for the diag. cause as i am sure you are aware of the cost of replacing all those parts is getting expensive!
Good Luck

 

thanks for the advise. I was looking around and i found a very small vacuum hose that was not on fully so i fixed that so i will give it a try in the morning if it is fixed. by the way i don't know if i mentioned that the vehicle runs perfect once it is warmed up only runs bad when cold.

 

I didnt know it ran ok when warm, you are going to need to look for codes and pids. Try to find someone with a reader... ALSO i said it last night and I will say it again, wrong oil will do that, be very sure if it is really col that you are running a good multi-grade 5w20 oil.
Good luck

 

Hi thanks for the comments. I do have codes popping up and and i am getting codes PO171 and 174 (which are running to lean in both banks). I have brought it in to a mechanic and he ran tests and nothing came up. The scanner says everything everything is running properly. I drove it this morning and it did the same thing, It starts fine then idles down, as soon as i start backing out it idles down to about 400rmp and shakes. You can here a popping noise in the exhaust. If i give it a little gas it runs great until i let off. It drive perfect down the road until i come to stop. Once my truck reaches optimal running temp it idles fine. Or if it is usually above 45 degrees. I will check on the oil it says to run 5w-30 in it but i will look into that more. please keep giving me your comments it can only help thanks.

 

2 gallons coolant, intake gasket kit, upper throttle body gasket , coolant out o-ring, an opportunity to clean your intake , injector slots(o ring seal), vaccum leaks on the inner side of the intake are hard to detect, oh yeah and about 6 hours of your time ,just might fix your issue IMO

 

I was looking at my DPFE sensor and one of the ports connecting to a hose looked corroded. I don't know if the DPFE sensor could cause an idle issue or not. I sprayed air in one port and nothing came out the other. I am unsure if they are connected or not. If so it is plugged.

 

egr system is inop at idle per pcm, unless your egr valve is slightly stuck open from deposits

 

I was talking to a mechanic and he told me that a failing DPFE sensor could cause a bad idle and pull the lean codes and not always pull an egr code. My friend has the same truck so tomorrow i am going to put his in and see if there is a difference. Also the reason why the one side of DPFE sensor port is bad is from a hose that fell off and i did not no at first so it would be sucking in dirt and whatever else. I appreciate all the help you all have been giving me, I am been kinda stressed out from this thing.

 

The dpfe will throw codes if faulty, but this is only active off idle, i could see the hose sucking in dirt and other things over time that would end up in the egr and then intake and so on, an egr slightly stuck open will cause a lean condition too much air with inert gas combo to fuel ratio, have you checked you egr system ? green line at egr should only have 0-1 ingh vacuum at idle, cleaned port from egr to throotle body, engine should stall if you apply vacuum to egr ( 5 ingh) you can do this with a hose and you mouth(suck test), but the onle thing that would affect idle is if the egr is slighly stuck open either by deposits or the evr is sending too much vaccum to egr (over 1ingh) at idle

 

Thanks for the response, i have taken the egr off before but i am unsure how to test if it is stuck open or closed. I will look into it more.

 

well i have good news. I finally was able to get my codes checked while my truck was idling bad. So when i checked the codes it is still running lean in both banks but also now i am getting a PO401 code (insufficient egr) so i am going to replace my egr today and hopefully that was the problem all along. I will let you know if it is fixed.

 

Hope that fixes it just make sure there is no vacuum above 1 inhg at egr form evr at idle and the dpfe hoses do not cross when connected, i hope the air pressure you blew into the dpfe wasnt to high this will damage the sensor, never heard of air being able to pass thru it, since i read that i tried a couple dpfes that i have lying around and i cant blow or suck air thru them, from what i know there are dead end pressure sensors,