98 F-150 5.4l

I am working on a 1998 Ford F-150 5.4L, it has a very rough idle, no CHECK ENGINE light/NO CODES.

I have replaced the MAF Sensor and still absolutely no change.

Running rough is allmost always an ignition problem.. If the wires have over 60k on them they should be replaced. Are the boots down over the plugs. Check the electrical harness to the coil. Could have corrosion. Check the PCV valve. It would cause what you describe if it is defective. It should rattle when shaken and you should be able to blow into it one way but not the other way. Check all the hoses for a vacuum leak.

5.4L engines have no wires they have Coil Over Plugs. (COP) I would run a power balance test, monitor each cylinder to see if any of them have a spike when you brake torque the vehicle. It may even do it during idle.

How many miles are on the thing. We have a 98 F-150 at work with a similar problem. Turns out that it has 70% leakby in cyl no.1.