Well, here goes. For Sale: 1998 F-150, 146k miles, cold A/C, Has ABS and CEL. $1700.00


Reader says P0401. Cool! My favorite. Pay the man $1500.00, and off I go.


Pull a vacuum on the EGR valve, no change in idle. Uh-oh, gonna be a dirty job. Pull the throttle body to clean it, and immediately notice it doesn't much need it. Reassemble.


Pull a vac on the valve again, no change in idle.


Check voltage at the DPFE. 1.3v, but doesn't change with a vac on the EGR valve. AH-HA! Pick up a new DPFE and start removing the old one. Sensor is oddly clean, like the throttle body. Somebody has been chasing this thing already. I put the new one on, know full well nothing is going to change. It didn't. 5v reference voltage IS present on bottom wire. Phew.


Went ahead and checked voltages on The Vac Reg Solenoid, and drove the truck with Vac gauge connected. Nice, positive drop to zero when throttle is released. Voltages all checked out.


I am completely stumped. Any suggestions regarding the next direction of my suspicion would be appreciated.