97 f150 4.6l 4x4
My truck started running rough at idle then when I am driving then slow down to stop the RPMs will drop below 500. Is there anything else that could cause this problem besides a vaccum leak. Or could that cause this at all. If I remember corectly the code says that it is a (exsaust resiculation flow low) error. It has also been hard to start at times. I have never seen this error before could use some help please!

 

401 code is low egr flow test.
I suspect you have more than one fault by your discriptions.
The idle is one and the 401 code is another.
First thing I would do is check out the EGR tract for being blocked with carbon.
Remove the EGR to check out the port into the..intake..for blockage. Test the EGR for operation and be sure the tube is open and crack free.
Clear the codes.
Then if the 401 code comes back, the DPFE sensor is suspect.
Take it a step at a time.
Idle speed fault may be the IAC needs cleaning.

 

I agree with Bluegrass. I think you have two seperate problems. IAC going bad and clogged EGR ports are the common causes. I would work the idle problem first since cleaning the carboned-up EGR ports won't make the truck run noticeably better, it will just get the light to go away.

 

I can take care of the EGR but I dont know what a DPFE or IAC are or were they are located would someone please explain this for me.

 

The IAC idle air control is located on top of the throttle body where the last large air intake hose connects. It has an electrical connector.
The DPFE is located and mounted by two small hoses to metal tube stand pipes off the main tube coming up off the drivers side exhaust to the EGR valve at the intake manifold.
It has an electrical connector.
Reference Haynes page 6-2 layout

 

Thank you Bluegrass i will check them out asap.

 

Could be a stuck open EGR valve. The DPFE sensor measures the change in exhaust pressure on both sides of a metered orifice. If the EGR is always open it isn't reading what it should on the DPFE and even when it opens, it doesn't change. This could also cause the low speed/low idle rough idle. If you've ever opened an EGR valve manually, u'll see that it does the same thing to the engine(cuts out and misses).....

 

A 401 test is only allowed after the regular EGR function has passed or the 401 test has no meaning.
For a 401 test, the program opens the EGR for a specified flow rate by pulsing the EVR control to get the calibrated opening flow rate. This rate is measured and reported by the DPFE. If anything causes an out of limit reading 2 times in succession, the failure sets the code and may turn on the lamp.
A 402 code is a pressure test with the EGR closed so the DPFE will read the same pressure on both sides of the orface. This test is done just after start up and does not depend on an EGR failure unless the EGR is stuck open. This test detects rusted/cracked main pipe, connecting piping to the DPFE etc first before the 402 test is done on each drive cycle.
It's all in a logical order.

 

could be egr solinoid problem-leaking vacuum to or not releiving vacuuum from egr on deceleration when vacuum is at its peak. that would give the code and the problem.
just "tee" into the vac line at the egr with a length of hose and a good vac guage and go fo a drive!

 

It's a good test to actually see the operation and when it happens.
Expect to see about 3 to 6 inches of vacuum depending on throttle opening angle and the accracy of the gauge.