Idling problems with a 1998 Expedition 5.4 litre

[2020]

This car has about 144,000 miles, and I have had no problems until now. I have had the Idle control valve replaced before. About 2 weeks ago, my check engine light came on.

The car was running rough, shaking, and idleing below 500 RPM. I had it checked and the codes showed that O2 sensors Upstream/downstream were to lean.

Replaced all 4, car ran ok for a few hours check engine light came back on. The car now idles up high then back down like it is about to go dead, but does not fall dead. Ran another check and it stills says it is the 02 sensors running lean.

I have not noticed any hissing for air/vacum leaks.

What could cause the test to show 02 sensors running lean after they have been replaced?

Need help...............

[goon]

make sure the intake is not leaking(sucking in air), look at the plugs and throttle body try cleaning it. Make sure the mass air flow sensor is not dirty, its located right at the filter assembly you can remove it to clean.

[asvare]

There is a vacuum leak all fords are known for this follow all the hard plastic vacuum lines from the intake/throttle body, pay special attention to the elbows as these are made of a low grade rubber and collapse or break down. the most common one is the one on the back of the throttle body. An old 90 degree spark plug boot will fix this problem is cost is of concern, if not I recommend buying a whole new assembly. Don't forget to disconnect the battery after repair to reset the KAM.

[2020]

thanks guys

[2020]

fix it bro THANKS ALOT!!!!!!!!!!

[JimR]

What was the problem?

[tbddj97]

The vacuume line next to the fuel line was collasped and had a hole in it. Whet to the local parts store and got a heater hose with a 90 degree bend and just cut it to fit. Fixed the problem and has a much better hose than stock replacement.