98 Ford Expedition idling rough

My 98 Ford Expedition just hit 100,000. The "check engine" light came on within a couple of days. Within a week, it began to idle rough and would drive rough when the engine was cold. I took it in to have a diagnostic reading performed which revealed about 5 different O2 sensor codes and a couple of "fuel too lean" codes as well. I have replaced the fuel filter, all four O2 sensors and the spark plugs. Have also put in fuel injector cleaner. The truck no longer rides rough, but still idles rough. The fourth spark plug had oil on the top where it connects with the ignition coil. Could the coil be the problem or could it be a fuel injector?

sounds like a vacuum leak to me, that's usually when you find the "too lean" code... sometimes a sticking EGR can cause this too...

use a plant sprayer full of soapy water, and hose down every gasket you can see on the engine.. if it's got a vacuum leak, you'll find a spot where the engine smooths out...

Thank you. I'll keep you posted.

Doesn't appear to have a vacuum leak. Someone suggested it may be a faulty fuel pump. The vehicle will run smooth then turn to very rough at various times.

I had the same codes come up and it ended up being a vacuum leak between the PCV valve and the back of the manifold.

Good luck.