P0171 + P0174 Code popped up but no RPM DROPS

[2000Xplor3r]

99 ford explorer xlt AWD v6SOHC vin E, today a code came on, and it was the infamous P0174 + P0171 code at the same time, nothing else came on.. Now i played under the hood doing my thermostat housing and coolant flushing ect... I didnt think i had a bad idle, cuz RPMS do not drop and my truck does not stall at all, but i do have a wierd Jolt through my truck at red lights or in park now im stumped could this be a bad idling problem because i thought it was a bad motor mount, hmm this is frustrating because i have looked at alot of the hoses but cant seem to find any cracked or bad pcv hoses, i cannot find the PCV valve on the sohc engine is this under the intake or in the back of the engine like farther back where the plug wires wrap around to the passenger side... ive cleaned MAF, throttle body, and have done the tuneups and basic things... my truck runs strong atleast from what i feel or think i dont see it wanting to die and does not struggle besides the idle jolt or idle vibrations like i said earlier... can anyone help me i have read multiple pages and cant seem to find someone with the same problems and hoping maybe they are related and figure these out.....

 

[2000Xplor3r]

i will add that when i step on the gas i can hear a whinding or like a whistle feeling from the middle of my dash recently or maybe im listening to hard lmfaooooo

 

[XLTrunner]

I'm curious...how did you replace the thermostat housing and not remove the upper intake manifold? Just did mine (referring to the complete housing ass'y) a couple wks ago and had the upper intake off the car...which clearly exposed the pcv valve and hoses at the rear of the intake. Sounds like you may have a vacuum leak. If you separated any part of the intake manifold, you definitely need to replace the gaskets or risk an air leak.

 

[Mike65]

I'm curious...how did you replace the thermostat housing and not remove the upper intake manifold? Just did mine (referring to the complete housing ass'y) a couple wks ago and had the upper intake off the car...which clearly exposed the pcv valve and hoses at the rear of the intake. Sounds like you may have a vacuum leak. If you separated any part of the intake manifold, you definitely need to replace the gaskets or risk an air leak.

On my wife's 99 Sport that has the 4.0 SOHC I removed the upper & lower thermostat housings to replace the by pass hose & did not have to remove the upper intake, it was a pain but it was doable.

 

[2000Xplor3r]

hey guys, hows it going when i did the thermostat housing i removed the Throttle Body and intake hoses to get to get to the upper radiator hose, and the thermostat housing... my 2000 AWD 4.0 SOHC i found the pcv valve placement today, its behind the upper intake manifold those big black tubes that the throttle body goes to, by my distributor with the plugs on it you can see the pcv valve placement and the ttops to each of the intake sides from the driver side standing over the engine bay with a flashlight, follow the two hoses on the backside of each the intake sides .. i dont know if its like this for the other models or years but the pcv valve does not need anything removed to get to it, this is waht i just found out in the last hour under the hood, its a 53 dollar part at ford for the pcv, the t top and the hoses that go to each side of the intake.... im just curious to other peoples problems codes and symptoms... any other thoughts here?

i never removed the upper intake manifold at all when i did the thermostat housing

 

[JusTheUsual]

Both banks lean. Usually its fuel pump or plenum gaskets

 

[2000Xplor3r]

i havent done the fuel filter at all yet, the plenum gasket your talking about the intake manifold gasket where the iac is sitting on, the gasket under the black tubes on the top part of the engine... the same two codes 0174 and 0171 code have come on twice both after being cleared and driven about 200 miles, the car has a big of a wierd vibration at red lights stop signs, in park... but the same codes keep reappearing i just want to see more ideas, pointers

 

[XLTrunner]

Yes...there is a set of gaskets between the Upper and Lower Manifold and between the Lower Manifold and block. They get old and hard after many years and are a common source for vacuum leaks. You mentioned that the Throttle Body was removed. Did you replace the gasket or gaskets when you did that? Should have been done. Still sounds like you have a vacuum leak by the symptoms you describe.

 

[JusTheUsual]

Yes the black things is the plenum or some people call it upper intake/manifold. Below that is another variable of words people call it that sits on your block, intake manifold, lower intake/manifold and so on. Like guy above me said about throttle body gaskets. It could be plenum orings gaskets, intake manifold/lower intake gaskets also are notorious to go on these engines. But if you haven't changed your fuel filter that could easily be the problem and the cheapest route to take if you don't have fuel pressure tester to see the fuel pressure. Which could be fuel pump also

 

[ylabblab]

p0171 and p0174 codes 2001 xlt 4wd 4.0 v6 sohc

Hi any luck I am having the same issue. I have replaced the IAC, The MAF, both upstream 02 sensors. Replaced the upper and lower intake gaskets but not the ones between the heads and whatever that piece is that the injectors sit in. I have looked for vacuum leaks and found none. I can not seem to find a replacement pcv valve. no longer made. I did take the pcv valve off and clean it. seems to be working ok. I cannot see where the large hose that the bottom of the pvc valve plugs into where it goes. looks like somewhere in the back of the manifold just can't see down there even with the intake plenum out of the way. fuel filter is not that old and fuel pressure at idle looks good 45 psi. What I did notice and this has been happening for a few years is when the air temp is 40 or below is usually starts up and stalls after sitting 8 hours or more. I if I cycle the key 3 or 4 times it will start right up. I have been told these fuel pumps when old get weak when they are cold. I am planning on replacing it soon anyway. I have 205,000 miles on it and try to keep up on repairs and maint. I may replave all the injector too just due to age. Not sure what to do next. Maybe take it for a smoke test?

 

[ranger7ltr]

Hi any luck I am having the same issue. I have replaced the IAC, The MAF, both upstream 02 sensors. Replaced the upper and lower intake gaskets but not the ones between the heads and whatever that piece is that the injectors sit in. I have looked for vacuum leaks and found none. I can not seem to find a replacement pcv valve. no longer made. I did take the pcv valve off and clean it. seems to be working ok. I cannot see where the large hose that the bottom of the pvc valve plugs into where it goes. looks like somewhere in the back of the manifold just can't see down there even with the intake plenum out of the way. fuel filter is not that old and fuel pressure at idle looks good 45 psi. What I did notice and this has been happening for a few years is when the air temp is 40 or below is usually starts up and stalls after sitting 8 hours or more. I if I cycle the key 3 or 4 times it will start right up. I have been told these fuel pumps when old get weak when they are cold. I am planning on replacing it soon anyway. I have 205,000 miles on it and try to keep up on repairs and maint. I may replave all the injector too just due to age. Not sure what to do next. Maybe take it for a smoke test?

Your fuel pressure is not even close to spec...Your engine is running very lean...It should be 65-73 psi and it doesn't vary with engine load...Changing the fuel filter and retesting the fuel pressure is in order...If the fuel pressure is still under 65 psi your pump or the supply hose in the tank would be next to be repaired or replaced...

 

[2000Xplor3r]

hey hows it going again, so i noticed that my motor mounts are looking like the 192k miles thats sits under the engine on each side they look compressed, i have a body vibration i can feel down the whole side or under my feet like a jolt vibration to the muffler, it does that in idle, park, reverse, drive as long as im stopped i can feel it like a motor mount, the idle does not skip a beat its always great does not dip, never stalled, i took the trottle body off to do the thermo housing and everything that was leaking... the hard black plastic behind the throttle body that gasket sits perfect, i never stall or have bad start ups at all, i notice that last night up it was cold and the truck had less vibration or jolting, but the mount feel was still present you can tell the difference cuz when i accelerate the truck runs great doesnt have hard time accelerating, the truck runs strong... i have not the whole pcv replacement it looks motorcraft original and they have the whole T-top and lines and pcv at ford for 55$ its one piece he says it pulls off goes right on... that and the fuel filter is the cheap route the filter is only 8 dollars i have the metal removal line tool already i should go do them both, but i think i have bad motor mounts and a vac leak, is there only 2 motor mounts on my Explorer and 1 tranny mount??? i was thinking of asking my shop i go to do the diag. test and smoke test and whole nine once the code reappears but the motor mount problem is annoying as can be what are some other symptoms of both problems mounts, and the pcv/or vacc leaks