1998 Grand Marquis engine misfires and stumbles.

My 1998 Grand Marquis misfires and stumbles all the time. The code P0401 that it throws indicates that it is EGR problem. The airway from the air filter to the plentum has been thoroughly cleaned, the EGR valve and solenoid have been replaced the computer reset and after about 50 miles the Check Engine Light comes back on.

Can anyone give me a suggestion?

Sounds like the passage in the intake is plugged with carbon, or the catalytic converter is plugged. This could be because of the engine misfiring all the time, or it may be the cause of the misfire- expecially if it has no power under heavy acceleration. Ignition coils are common failure to cause misfire on this Ford engine.

The ignition coils were common to fail on these, but also when this Ford engine gets a lot of miles on it, the EGR passage in the intake manifold would get full of carbon and cause that code.

Only way to fix it was to remove the intake manifold and clean it out. But that was only temporary as the engine burning oil will plug them up again.