So I recently acquired a 2002 F-150 4x4 super crew with the 5.4 V-8. It idles rough (surging from 400 - 700 rpm) when cold, and sometimes dies, but more often then not it stays running. It runs and drives fine when the accelerator is pressed and when going down the road. When it gets up to operating temperature, and has been there for a while, it seems to idle fine 95% of the time. The codes I have are P0136 (bad circuit to O2 sensor), P1151 (HO2S detects lean mixture or something like that), and the infamous P0171 and P0174, which is lean exhaust/mixture on both banks. Now I have read extensively on the internet about these symptoms and have done the following:

Sprayed every vacuum hose with carb cleaner, and even around the intake manifold and injectors.

Considered the IAC (its new, the guy I bought it from replaced it a couple months ago)

Torque app for android phone says vacuum is good.

Cleaned the MAF and air temp. sensor with electrical cleaner

Checked all of the vacuum hoses on the engine by pulling them off

Put grease around the fitting where the PVC valve attaches to the valve cover. Seemed to make it idle a lot better after messing with it, but I don't know if it was a result of the engine being fully warmed up, or my messing with the PVC.

Does anyone have any suggestions on what to try next? I'm close to just dissecting the top part of this engine and seeing what the intake manifold gasket looks like..or could it really be an 02 sensor?

Thanks in advance, and Happy New Year everyone!

 

You did check the PCV hose elbow around the back of the intake, didn't you? It amounts for the vast majority of instances of this symptom.

A useless endeavor, if you were expecting to hear a difference by ear. The computer is too fast.

The Torque app has no way of determining that since there is no sensor on the engine that directly measures manifold vacuum. If it's displaying any such PID, it's probably an inferred (calculated) value derived from things like RPMs, TPS and MAF measurements.

Hook the Torque app back up, make a custom screen with gauges for the short term fuel trims only (or the upstream O2 sensor voltages), then monitor those gauges while spraying around. When the spray hits your vacuum leak, which you surely have, the gauges will spike and then slowly settle back down.

A recent thread either here or on one of the other F150 boards, found his 5.4's manifold had a crack. Since your drivability issue seems to stabilize when the engine warms up, it does sound like something is contracting in the cold causing a leak and then, when the components expand slightly when warm, closes back up. My 2.5L Conturd just got a new set of intake gaskets this fall for that very issue.

 

I did take that hose off coming from the PCV and into the back of the intake, and it appeared to be in good condition, and seals up good on the intake side. The PCV side of the hose, where it goes into the valve cover was a little loose and I put some grease in there to help it seal up. I'll try that torque app again and do what you said with monitoring short term fuel trims. Is there a way to test O2 and HO2 sensors with that app? A buddy of mine has a professional diagnostic tool that may be able to do that. I still think it is an air leak like you said, probably intake manifold related, but just wanted to officially rule out the O2 sensors.

 

Just did a few tests with a code scanner I borrowed from a friend. I looked at the STFT and LTFT and also simulated a rich condition to test the oxygen sensors. The STFT was 2.4% to 3.2% for both banks before spraying carb cleaner around the intake manifold. Then bank 1 jumped up to 53% for a couple seconds after spraying the passenger side, and went back down. Then it jumped up to 53% for a while and stayed there. I think at this point the engine had warmed up because it started to idle smoother. the LTFT was at 8% for bank 1 and 30% for bank 2 when at operating temp. The 02 sensor test i did was from this site: Part 2 -Troubleshooting P0171 and P0174 (Ford 4.6L, 5.4L) and it is towards the bottom under "test 2". The site told me to spray some carb cleaner into a small vacuum hose to simulate a rich condition..upon doing so, both 02 sensors for banks 1 and 2 went to .87 volts, which is supposed to be good and mean the 02 sensors are working fine. So I think that it is a vacuum leak, probably an intake manifold and/or injector o-ring leaking. What do you all think of these test results?