Hey guys,
Check engine light came on again. Had the code pulled, and it was P0401. Something to do with exhaust. I dont see a loss in performance much. A slight drop in gas mileage, but nothing huge. Any ideas on what it could be?

 

What do you drive? 74 Ford pinto? Motorized wheel chair?

EGR problem. Maybe clogged ports? You might need to take the TB off and clean them out.
If that doesn't work, I'd suspect DPFE sensor

 

X2^ especially if the dpfe sensor is the original aluminum one.

 

My bad,
99 4.6, all stock and original.
Any particular way to clean the ports? How hard is it to take off and put the throttle body back on?
Any idea on what kind of affects this willl have on it?

 

4.6 is common to get clogged ports that will cause your issue.

It's not difficult but will take a couple hours. Don't drop anything!