I have a 99 5.4. Sunday night I changed all 8 spark plugs, drove the truck monday it seemed fine, ran really good actually. Yesterday, tuesday I had my Pacesetter shorty headers installed. When I first started driving perfomance felt the same but I have some kind of Intake/Throttle Body noise. I have a P0401 code as well. The motor just sounds like its sick and almost starving for more air. Today the motor just feels really sluggish. I read some info on the headers would take away from the low end torque...I didnt think it was this bad, I will put the stock ones back on. I need to get it fixed asap Im wanting to travel with the truck this weekend and want it running better. I am waiting for my air filter to dry, it was fairly dirty.

Anyone know??? Thanks

 

I think the code is for the EGR valve. You might need to get a blocking plate or get the ECU reflashed. Don't hold me to that though

 

hmm if its not getting any air, might be in the throttle body itself, or intake. depending if they removed it while installing headers.