Need help.. Rough Idle in Drive but not in N or P

[Nemesis121]

I recently purchased my 99 Expedition and had no ciue of the prior service that was done on the vehicle. Its a 4.6l XLT and was running fine prior to me servicing it, but of course I decided to replace and clean alot of parts not knowing if any maintaince had ever been done. After replacing everything I started it up and it idles fine in Park as soon as I put it in drive it has a really rough idle, put it in neutral idles fine again, Reverse, 1 and 2 are the same rough Idle as drive.
Heres the long list of parts replaced

- oil pan gasket
- timing chain, guides and tensioners
- timing cover gasket
- harmonic balancer
- idler pulley
- tensioner pulley
- belt
- valve cover gaskets
- positive crank case tube
- crankshaft sensor
- camshaft sensor
- water pump and fan clutch
- upper and lower intake manifolds
- spark plugs
- knock sensor
- fuel injectors
- fuel filter
- DPFE
- EGR Solenoid
- DPFE hoses
- IAC
- Cleaned throttle body and EGR inlet into intake ( was completely blocked)
- thermostat

As i said it started fine and idles fine. its just when its in gear does it have a rough idle. The Only other thing I can think that it might be is the TPS, or some vacuum leak I havent found yet. Also checked the transmission fluid, ( Transmission was replaced 15,000 miles ago) it was a little low added Fluid but it didnt help. Also there are no Check Engine lights on the dash and the computer isnt throwing any codes. Thanks for any input

 

[Bedrck47]

Make sure you reconnected all hoses and also plugged in all connectors and that the connectors are seated properly

Recheck the DPFE hose's and make sure they are connected correctly and the connector is connected tight

I Know I said it twice Reason is I did the same thing once before.

You said you cleaned the egr. Did you remove the throttle body to do this??

Being its a 99 with 4.6 recheck the spark plug wires to make sure they are on the correct plugs

 

[Nemesis121]

I actually had no intension of replacing the DPFE and Solenoid so I originally installed the old ones, then thinking that these might have been part of the problem i installed new ones with new hoses. Also I when i replaced all of these parts I took everything apart and soaked alot of things overnight, to get rid of the carbon build up. Ive removed the intake manifold and all components attached 2 times now and reinstalled trying to track down the problem. Some of the smaller vacuum lines looked brittle but no noted cracks, but i plan on replacing them tomorrow. Im just wondering if i might have damaged the Throttle position sensor when i was cleaning the throttle body( didnt soak throttle body just cleaned with carb cleaner) Also i havent replaced the EGR valve bc it rusted onto the exhaust tube and ive started to round the nut trying to remove it. One more thing when I said i replaced the upper and lower intake manifold i originally had the aluminum upper intake and plastic lower (lower intake was cracking) the only replacement parts i could find were the redesigned upper plastic intake and lower aluminum intake. Could this be part of the problem? Thanks again any input at all is greatly appreciated.

 

[Bedrck47]

Take and spray some carb cleaner around the hoses If you have a vacuum leak you will see an increase in rpm's

What are the idle rpm's in neutral and in drive

 

[Nemesis121]

I'll give the carb cleaner a try, the RPMs in neutral are right around 900, in drive its 700-1000. The RPMs dip down and revs back up.

 

[1955moose]

Sounds like the first thing to check is intake gaskets you changed. Spray some wd 40 around gasket surfaces, engine will smooth out and have a friend look at exhaust, smoke will come out back if and when you find intake leak. Do the same to egr gasket and all vacuum hoses. How does truck run when you drive? Any missing under load?

 

[mr49erguy]

I know that this is a bit of an older thread, but I'm having the same exact issue as of today. I have a 1998 5.4 Expedition and it started running rough at idle when I'm in Drive. When I'm in Park it evens out, albeit a bit higher than I would like (1300 rpm). When in Drive or Reverse it idles down to between 1000 and 1100, which I am thinking is about 300-400 rpm higher than it ought to be.

I've had the truck for 3 months and I've cleaned the throttle body and checked the coils and plugs, but they looked like they were in good shape 2 months ago. I've also replaced the IAC as I was throwing a P1506 code. Replacing the IAC did NOT solve my issue, but I am going to check that the bottom nut is tightened down properly later today. I have a gut feeling that this may be allowing extra air into the system and causing part of my issue. I am also concerned that the TPS may have been damaged when the throttle body was off for cleaning a couple of months ago.

All in all, this feels like a vacuum leak issue to me, but I cannot seem to locate any obvious leaks when spraying carb cleaner around the normal spots that a vacuum leak my be.

I took it out camping on Friday night and she was running great and today out of nowhere the issue with the idle in Drive has got me a bit worried. All thoughts are welcome at this point.

 

[thenaaks]

There's a vacuum trunk line wrapped in loom that runs into the passenger side of the throttle body. There are 3 or 4 smaller lines inside the loom, and going different places. I've found several of those lines cracked on various fords. Check those really well.

 

[mr49erguy]

Thanks thenaaks! I checked as many of the lines surrounding the throttle body as I could this afternoon and did not see anything unusual, but that does not mean there is not a problem still.

I connected up the diagnostic tool as well and I have a P0304. Meaning Cylinder 4 has a misfire. Wow! Of all the cylinders to have an issue it had to be #4. I'm guessing there is coolant dripping into the COP and corroding it, causing the misfire. I do not have the time nor the patience to try to get to replacing the COP on cylinder 4, so I will be taking it into my local mechanic this week before heading out for some camping over the Memorial Day weekend. I will post the results after taking it in.

 

[thenaaks]

#4 stinks. Especially with rear heat.