Hi,
I drive a 98 F-150 Ext cab 5.4 litre V-8 4x4 truck.
Engine Light came on last week. I stoped by AZ and codes thrown were for ALL 4 O2 sensors, MAF sensor and possible EGR valve.
I was shocked!
Anyway,
Replaced 3 banks with Bosh o2 sensors (#1 bank was replaced a few months ago) Thought I would try the other 3.
Engine light went out after resetting it.
However....
The engine is idling erraticaly AND Loping!

A little background on parts that may affect this ...
Plugs and wires changed less than 6 months ago,
Air Filter Changed 4 months ago.
Fuel filter changed 4 months ago-Cleaned it this weekend- no dust
MAF Sensor changed this weekend, along with 3 O2 sensors.

I think I changed the IAC sensor like 6-8 months ago too.

I did notice a hole in the exhaust where they come out and split into the dual exhaust.- Right where the weld is. I had them put in about a year ago, But I live on a gravel road, and they have to be replaced almost every 1-2 years anyway.

Like I said the Engine Light went out.
I added a bottle of STP gas treatment today after filling up. Have only driven it 20 miles since.

In the driveway this morning after returning from school, it was missing badly at idle.
I let it run to see.
It would begin to lope, the RPM gauge would drop to about the .5 mark, then it almost went dead, then it would catch back up and stay between the .5 and the 1 RPM mark. constantly bumping up and down 1 tic mark( like the .7 and .8 mark) on the gauge untill I finally turned it off.

This afternoon, Went to school, While in line for pick up, the truck seemed to idle high, at the 1 RPM mark the entire time, and sounded like it was idling high the entire 10 miles home.... Until I turned on our road and stopped at the mailbox, Once again, It began to idle erratically and lope, the RPM,s would drop drastically all of a sudden, but before going dead, it would catch back up and continue running bad and missing. I turned it off. So it has not actually went dead on it's on, I have turned it off manually every time.

I checked the EGR valve, vacume lines and connectors.All seemed ok

Does anyone know what this is? Or is my information confusing?

I have a Haynes Manual. I know there are a few more things to try.Fuel pressure chack... etc. I was hoping someone may could tell me what they think it may be before I spend too much more money on it.

I am also in the middle of a timming belt change on a PT Cruiser(water pump, tensionner, all belts, Hoses too and that is getting expensive alone.
(there is a real GOOD reason the shop charges $1200.00 for THAT job!!!)
anyway, back to the trucks problems..

I sure don't want to pour uneccesary money into the problem.

ANY advice would be greatly appreciated. Thank youi

 

That was the AIR filter I cleaned and checked for dust,,, not the fuel filter LOL
Sorry bout that

 

Sounds like AZ got you. You most likely have a vacuum leak (pcv hose) that gave you the "O2 codes", a faulty DPFE sensor/clogged egr ports which gave you the "egr codes". Those stores pull a code and automatically try to sell you whatever part matches the code. Codes are like a road map, they lead you in a direction, not automatically a failed part. A vacuum leak will cause your idling concern about it loping. Like I said, it is usually the pcv elbow behind the throttlebody. Good luck.

 

I also had this problem on a 2003. I could here hissing from a vaccum leak which I found. It was on the pcv elbow behind the throttle body. I could put my finger on the hole and the engine would idle fine.Youmay have to take off some plastic covers to get to the elbow.
Good luck