P0174 code that will not go away

[coax31]

New to this site but I have already leaned a lot. I have 98 XLT 4.0 SOHC with 181,000 miles. I have this CEL P0174 code (bank 2 lean) that will not go away need help diaganosing this. It idles rough when cold but levels out ok when warm.

I have already:

- Cleaned the IAC, under the black cap, felt pieces and all.
- Replaced the #2 O2 sensor.
- Had the upper intake plenum gaskets replaced

What else should I do ?

Test for clogged fuel filter/pressure?
Clean\replace MAF?
Try to find a vacuum leak somewhere?
Replace the lower intake gaskets?

 

[yeah61794]

just a crazy question, have you reset the computer after doing all these things?

 

[2000StreetRod]

one bank lean

Since only one bank is lean, unless the mixture is just at the limit, it's probably not the MAF sensor or fuel pressure. It's probably either a leaking hose or gasket(s) on the driver side. Most of my leaks were from the gaskets between the heads and the lower intake manifold. Before replacing them I would check the hose from the PCV valve to the upper manifold, the brake booster hose to the upper manifold and the hose on the bottom of the upper manifold about half way back from the front with the plastic insert keeper. You can see it in the photo below between the engine harness main connector and the oil filler cap.

 

[coax31]

just a crazy question, have you reset the computer after doing all these things?

Yeah i had it reset and it came back on, after i had the upper plenum gaskets installed the CEL stayed off for 130 miles, then I had it it reset at the auto store and it came back on after 50 miles.

 

[coax31]

Since only one bank is lean, unless the mixture is just at the limit, it's probably not the MAF sensor or fuel pressure. It's probably either a leaking hose or gasket(s) on the driver side. Most of my leaks were from the gaskets between the heads and the lower intake manifold. Before replacing them I would check the hose from the PCV valve to the upper manifold, the brake booster hose to the upper manifold and the hose on the bottom of the upper manifold about half way back from the front with the plastic insert keeper. You can see it in the photo below between the engine harness main connector and the oil filler cap.
View attachment 57699

Thanks for the info, I checked the hoses and sprayed starter fluid on them they all seem ok, would a bad PVC cause this error? I might have to change the lower gaskets next to the heads.

 

[2000StreetRod]

sticking PCV valve

The air that flows thru the crankcase is metered air. There is a T above the PCV valve that distributes the crankcase fumes to both sides of the upper intake manifold equally. A stuck open or closed valve should not affect the mixture only on one side.

 

[coax31]

Thanks for all of your help, I ended up getting all the manifold gaskets replaced, it was the lower gaskets that were leaking, now it runs like a champ at 183,000 miles. no more CEL

 

[2000StreetRod]

Congratulations!

And thanks for posting the solution.