Running Too Lean

I have a 1998 Ford Expedition XLT (Eddie Bauer) 5.4 engine with about 60k miles on it. I got a check engine light which turned out to be bank 0 and 1 reporting running "too lean". This was explained to me that there is not enough fuel, or too much air in the combustion.

At the time, the car was not experiencing any odd behavior, but wanting to prevent any potential problems I decided to replace the fuel filter since I didn't know the last time it had been changed. After replacing the filter the car stalled for the first time. Ever since it has been off and on, having difficulties idling. It will drop from 1k RPM to 800 to 500 and sputter and sometimes stall. If I give some gas to increase the RPMs, it will sometimes help, but sometimes I can still hear it sputter (like it's running too lean).

The next inexpensive (?) step was to replace the O2 sensors. Since I wasn't comfortable with doing that, I had a local shop replace them. I also had them clean the fuel injectors and lines. The problem seemed to go away after a time (we assumed the computer had reset), but then came back.

From what I've seen online it seems that the next step is to check the IAC or the TPS sensors. I saw one post that chastized the "random replacement of parts" in an attempt to diagnose the problem. Is there really a way to test these sensors without replacing them? With a diagnostic code "Running Too Lean" which could be cause from 10 different sources including bad sensors, what is really to be done?

I'd love to hear from someone who has had a similar problem and was able to fix it. This is just one more reason why I don't like Ford's. My previous problem was a "misfire" on plug #4. Ford decided it would be a good idea to require dropping the engine before the back plugs can be replaced. Good grief - on a F-150 body, the most common service duty truck in the US? What design wizard came up with that?

Thanks for listening to my rant. I'll post again once it's been fixed.

 

I would start by cleaning your MAF sensor. It's located on your intake tube near the air filter.

I would also check fuel pressure. A failing fuel pump will causing your problems as well.

 

What you really need is a good flow chart detailing which components and in what order you should check them. Best place? AllData, but you'll have to purchase a 12 month subscription for all the goodies. This is the same info professional garages use (except they pay big $$$ in order to have info on ALL vehicles).

Fuel pump pressure been checked? Just a thought.

 

Great minds think alike.

 

Hello and welcome to the "Wonderful World of Ford".............Look for your PCV valve..........Follow the plastic lines back towards the intake.........They are HARD plastic till you get to the connections..........The "elbows" over time collapse and tear.........That's where you'll find your leak and your problem

 

Yes, one shouldn't throw parts at a problem
Most often, there's no reason to replace good parts to try and fix a problem
And just about all of the sensors can be tested

As for your specific problem, you should post up the exact code
(An "O2 code" or "Lean code" don't necessarily mean your O2 is bad or you are actually running lean)
And as you now have other problems, have them read again and post them up
There may be changes/new ones

Even a lack of codes tells us something

As for other stuff to check, I wouldn't try the TPS or IAC at this point

I'd clean the MAF sensor (not the screen, pull out the sensor...you may need to make your own slots in the screws, they may be "tamper-proof")
I'd also look for any un-metered air entering the intake (loose, cracked tube), and vacuum leaks along the tubes elsewhere-especially at those elbows, they can develop cracks that are very, very, hard to see