98 Expedition won't idle

Does it idle ok when it's cold? If it's only when warm, try testing the EGR. Or try cleaning out what you can of the intake system. (Throttle body, and accompanying vacuum holes) I'm assuming that you pulled the battery after replacing the idle air and o2's, to reset the computer. Sometimes that can make all the difference. Also, does it idle ok in park, and only low idle in gear?

Thanks for the help. No it does not idle when cold except for about the first 15 seconds. It doesn't idle in gear, park or neutral. Thanks for the segustion on resetting the computer by removing the battery. I assume, disconnecting the battery for about five minutes should be enough. I'll check and clean the air intake. How do you test the EGR? Could it be low fuel pressure? How do I test the fuel pressure?
Thanks again for your help.

Well generally an EGR problem is only when the vehicle is already warm. And unfortunately i'm not familiar with your particular truck, but maybe this link might help a bit. http://autorepair.about.com/cs/troubleshooting/l/aa042603a_10.htm

And yeah, 5-10 minutes with the battery off should be good to make it relearn. Forgot to mention that you wanna let it idle for a few minutes afterwards to let it figure things out.

If it doesn't idle correctly ever, then i'd say it's most likely a vacuum leak, a fuel pressure problem like you said, or an ignition problem.

Fuel pressure can usually be checked at the fuel rail on newer cars, kinda looks like a tire stem. You might be able to borrow a pressure gauge from an auto store. But make sure you get a high PSI fuel one, and not one for a carbuerated engine. (lower psi) You'll have to see if you can find out what it's supposed to be at while running...sometimes you can check it without running the engine, and just putting the key to on to power up the pump. Obviously if it's out of range, and you've replaced the filter and regulator it pretty much leaves the pump or maybe even clogged injectors. Also a possiblity of a pinched fuel line. Did the fuel that came out of the old filter look funky?

Best of luck!