Q: Throwing codes P0300 and P0401 on 2001 Ford Expedition

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We have a problem with our car running rough. Sometimes it drives fine, and sometimes it drives really rough. We have replaced the EGR valve and two out of the eight coils. (Had a code before and it was specific to #7 coil, and basically same behavior) It is very frustrating trying to pin down one thing as to what it could be. We are thinking about just changing out the rest of coils and see what happens with that.
(1) Answer
First -- P0401... Very likely has a faulty EGR position sensor. This is common on these vehicles, and is an easy replacement. Ford even had a program to replace these free of charge, but this has expired on your year and model.

Second - the P0300 - this is the random misfire that could be any of the cylinders. A definitive test would be to perform a Power Balance test and see what cylinder(s) drop out.

If a diagnostic tool that can perform the test is not available, then I would recommend replacing all the plugs (if you haven't already) and all the boots for the coils first. Retest. If the problem returns, it would be a shame to spend all that money for all new coils when it is probably only one that is failing.

Good luck.