Got the dreaded 0401 on the 1998 F150 2WD. Replaced the EGR, and DPFE, with no change, then discovered the carbon buildup in the throttle body as discussed in this forum. We got that all cleaned up. Now 0401 is gone, but we are seeing 0402 and very rough idling. I assumed the EGR solenoid was bad, so replaced that with no change. Vacuum is on the EGR all the time, even at idle and I do not think that is correct. When we pull the Vac line off the EGR, it smooths right out & runs great. Any ideas what to try next? I am thinking PCM?
Thanks!

 

You need an EVR. Just keep it disconnected until you get one.

 

We had changed the EVR, with no difference in behavior - vacuum is on the EGR all the time - even at idle We have it disconnected so we can drive, but I cannot get it inspected until I get it fixed.

 

It's either the EVR, - vacuum lines connected wrong, or a bad PCM.

What color are the lines , - any pics?

 

Well - this is embarrassing - went out to take pics & Vacuum lines to EGR and booster were reversed : )
Thanks for your help - you got me going in the right direction.

 

No problem lol.