Hey All, im hoping someone can shed some light on a problem im having with my all stock 04' 4.0.
So, all of a sudden my truck runs like crap. I'm in NYC and its been really cold and I just don't drive the truck but a few times a month, with the exception of moving it from side to side for the "street cleaning". Yesterday, I went to take it for a drive as soon as I started it the motor was running rough and it seemed like the exhaust note was louder and the truck was shaking...I popped the hood and the motor was kind of bouncing around and the idle was erratic. I was thinking maybe its just really cold and once it warms up it'll get better.. it seemed to smooth out a little. HOWEVER, when giving it more than 1/4 throttle its sputters like its running on fowled plugs, and has no power(relatively speaking for a slow-*** truck). When I returned back to the city and parked the car i popped the hood again and the motor is still bouncing around. I was just staring at all the little hoses and sensors and decided to pull the vacuum hose off the top of EGR valve and then the motor and idle instantly smoothed out. I haven't driven it yet to confirm its fixed but was wondering the mechanics of what i did and what happened. Thanks

 

Also, I ran my OBDII scanner and the only codes its throwing are for front wheel speed sensors

 

How many miles on the '04?

There should be no vacuum to the EGR valve at idle, so............

When you pulled off that vacuum line two things happened.
1. If there was enough vacuum on the hose then EGR valve was open and exhaust gas coming in at idle, and above, this was causing the rough running.

2. Now open vacuum hose added more air to intake allowing better fuel/air mix that was too rich.


Next time try putting your finger over that vacuum hose to see if #2 is true.

The EGR valve gets it's vacuum thru the DPFE sensor, it will have two vacuum lines and an electrical connector.
Computer opens vacuum to EGR valve via the DPFE sensor only when engine is under load, cylinders heat up under load, the exhaust gas cools them down, as odd as that sounds, lol.

DPFE sensor can be tested but if it is passing vacuum to EGR at idle then it is probably bad, but volt/ohm meter can be used to test it.
Normally you would get a code if DPFE sensor had failed, but if the valve inside it has failed the computer wouldn't know that

 

THANKS for that informative reply!!!! Ill do some research and post what I find.

 

Also just as a "heads up" the PCV valve vacuum lines on the Fords are failing/cracking after 10years, the elbow is the main place for the failure, remove it to check it.

 

I will check those too.. Thanks.