Negative. Other places in this forum state that there are multiple lines coming off the PCV tube. Mine is a single tube from PCV to back of throttle body. There is a group of 3 vacuum lines that T together right above the PCV: if my memory is correct, one goes to another T at the passenger firewall, one goes to the vacuum release thingy near the EGR, and the other goes into the left side of the trottle body. When I said it wasn't connected, I meant that it is not part of the PCV vacuum tube. Sorry about that.

My mechanic is going to take it and check every vacuum line, the inside back of the throttle body/throttle plate, the EGR, and the vacuum release thing. Hopefully he can find something!

I'll report back what he finds. Thanks, Jim!

 

My mechanic checked every vacuum line and did not find a leak. He sprayed all around the manifold gasket. No leak. Ran a smoke test. No leak. Lines from throttle body to EGR are clear. EGR/DPFE are good. Computer is not throwing any codes.

He's going to check for excess back pressure next.

Open to suggestion of what else to check. Perhaps a sensor is failing enough to cause a rough idle, but not failing enough to throw a code?

 

Ok you have lean codes . MAF sensor good ? No vac leaks ? Good fuel press ? How about ethanol content or water in fuel , I see a lot of that where I work .

 

MAF sensor swapped out. No change. No vacuum leaks. Good fuel pressure. I ran a full tank of 'real' 91-octane gas (no ethanol) with seafoam, and another tank of premium (but with ethanol) with seafoam. No change.

 

I should also add that my mechanic did a compression test, and all cylinders were fine. Not as good as new, but no single cylinder was off by a drastic amount. He checked each coil pack while it was off, and each one ohmed out within spec.

 

Ok , No vac leaks , good fuel and pressure . Base engine , good ? . No excessive EGR flow ? Maybe o2 sensors are not reporting correctly ? I don't remember if you have looked at them . It runs bad , correct ? Can you graph and compare both front and rear o2 sensors ? That could help . Maybe you have bad info going to the ECM .

 

I came to this page and read a lot of possibilities. but all the air leak and O2 sensor talk didn't logically follow - if these things were the problem they would occur when it was warm as well. I went ahead and measured fuel pressure (OK) but replaced the fuel filter (possible water collection freezing and reducing flow to pressure regulator which I also replaced while I was at it). NO Change! Followed the logic - MAF or Intake temperature sensor is not working correctly - data is posted for the temp sensor but I just bought one and waited for cold - at -5 and after warm up in close loop it started idling rough -- pulled over yanked the old sensor out - need vice grips and installed the new one - FIXED. Have had a slight episode or 2 since - Rev engine in neutral - problem goes away - I try to keep tank full to avoid water accumulation and put Heet in it as well. Will also look at the MAF sensor - it is original 160K. I have a temp read out in the expedition and notice over the hill and hollers the temperature varies quite a bit - some times 20 deg in just a few miles.

 

I have a 1998 expedition, 4.6 eng. Have been getting 171 and 174 codes. Also a misfire on number four cyl. Replaced spark plugs, that repaired the misfire. Found a broken vac line going to the valve on the port (for Navy guys) or drivers side for normal folks, fuel rail. Couldn't find any other leaks at present. Went for a drive and ran like new. Then after a stop or two, ckeck eng lite came on again. Ran OBD when I got home and 171 and 174 codes came up. MAF appears to be clean and temp sensor appears in good shape. Haven't attacked the pcv system yet. Any other suggestions? Where can I get values for OBD readings?

This is a great forum by the way!!http://images.ford-trucks.com/forums...ies2/thumb.gif

P.S. Car has 140000 miles on it. We bought it used in 2001, and had 65000 on it then. Great condition. Air suspension on rear and it still works super!

 

Follow the PCV line to the back center of the intake. Very carefully inspect the elbow you find there.

 

Yes ! check for Vacuum leaks ! Also , if running lean , Maf reading at Idle should be engine displacement . So a 4.6 should read 4-5 gps at idle no load with ac off , 130-150 at wot ,min. Best of luck !

 

Hey... thanks for all the help on this issue. I have an easy fix for anyone else that's dealing with it.
The vac line that goes from the rear of the eng (4.6) is fairly easy to get at. The line that goes behind the eng to the pcv valve is the problem. So, what I did was get the 90 degree for the main vac at the back of the eng. then I got some poly pipe (which is rigid but can be softened in warm water and bent). I made it go across the top of the eng rather than snake it through all the jungle of wires and pipes behind and forward to the pcv valve. Now if I get the same codes I can get to it quickly and easily.

I live by the KISS principle. (Keep it simple stupid). I am not saying anyone is stupid, that was what the Navy folks would say...LOL

Again, thanks to all who chimed in and helped.

 

Ok so this is my first go at asking for advice on this forum. I have a 2001 ford f150 xlt. Its got the 5.4l and is 4x4. I have been having issues with the codes and getting the problem fixed. The cel is on and shows both bank1 and bank2 running lean. I have replaced the elbow and the egr, replaced all the rubber hoses on the vacuum lines. I even replaced the air idle control solenoid, the mass air flow sensor, throttle position sensor and the fuel regulator. The fuel pump is fairly new, i replaced it about 6 months ago. Everytime i replace a sensor and clear the codes it seems fine. But the other day it was running perfect until a cold front blew in while i was at a restaurant. The drive it started axting up again. Surging when in park or idling, dying at stop signs and lights. Its driving me crazy. I am curious about maybe the "engine coolant temp sensor" or a "cylinder head temp sensor"... please help me out with this thanks in advance

 

Leaking intake manifold gasket(s). The parts contract in the cold and open the leak up even more. That's why it's worse when cold and not so bad when warm.

 

Ok guys i need help. I have a 2001 f150 xlt 5.4 4x4. It has been a nightmare! First i was getting codes for p0171 (system 1 lean) and p0174 (system 2 lean). I have replaced AIC, MAF sensor, Fuel regulator, throttle position sensor, and recently the air charge temp sensor. I have done the ford drive cycle trying to get evap system to ready, but instead now with the CEL off my scanner reads P0171, P0174, and P0455. And after having autozone scan the codes to see what their computer suggests. Which the guy said maybe gas cap but that he didnt think that would cause lean codes. Backing out of the parking lot the truck died. All the way home the ABS light would be on flickering off occasionally, the truck would surge, ( like if the brakes kept getting pushed) all the gauges would fall or jump every few seconds. I made it home still with my CEL light not on. my scan tool still only shows P0171, p0174, and P0455. My CEL does work believe me this is the first ive read the codes with the light not on... please help!! Im about ready to set fire to it

 

Did you check the infamous PCV elbow at the rear of the intake manifold?