My 98 f150 every once in a while will idle really low to the point that it shakes the whole truck but this only happens 1 out of every 10 times i drive it. It happens most often when i get ready to back my boat into the lake after i have pulled it for an hour. I also have a check engine light for code 402 EGR. Are these things related? Will it hurt the engine to keep driving despite having the check engine light on for code 402?

 

The 402 code is detecting EGR flow when there should not be any.
This will affect idle quality to a large extent depending on how much is leaking past the EGR into the intake.
The cause can be the EGR it'self, the EGR regulator applying vacuum when it should not.
The DPFE detects this condition but it should not be the problem in this case.

As an extra item, after this is cleared, I would clean the Intake Air Controller to be sure it is not sticking and adding to the overall problem.
An easy one to fix. Good luck.

 

thanks i'll do that

 

Where is the air intake controller on a 98 f150 4.6? So i clean that out and take the EGR valve off and clean those passages and it should fix it?

 

actually this is just a question on top of this one. i have a 97 f150 that does the same thing. where is the egr valve?

 

I have the same issue at times, x2 on smakles question. I know where the valve is just how do you actually "clean" it?