Rough Idle in gear

[kngthn76]

Just picked up a 2004 Expedition XLT 5.4 this past weekend with 122,000. Idles smooth in park and neutral but idles rough in gear while sitting still. No check engine light. I bought it from a dealer and the motor was cleaned. Thought I would add that. Where would be a good place to start?

 

[svtl919]

coil or boot
does not always show cel

 

[kngthn76]

Bad coil or just not seating right. I have wondered if there is water in between the coil and plug. I plan to change the plugs soon. I have went 80 miles after fill up and it is on half a tank right now. I didn't buy it for the gas mileage but damn.....

 

[1997SCEBFEX]

Sir, Welcome to the forum.

+1 on poss water intrusion. would also clean/replace idle air controller.
PanHandler.

 

[kngthn76]

Thank you for the welcome. I think I will just replace the IAC along with PCV and fuel filter. Have to get the wife to release the funds. LOL

 

[1997SCEBFEX]

Have to get the wife to release the funds. LOL

when you crack that code, share

 

[kngthn76]

I am still trying to crack that code. Have to base it on safety or drive-ability issues. "If I don't get a cat back system, the Expedition will clog up dear"

 

[kngthn76]

Here is the update on the Expedition. The molded hose that runs into the heater core has a small leak under pressure and coolant was filling up the spark plug holes. The leak was small enough that no coolant ever hit the ground. The coolant ate the coil pack boots and caused spark issues. My mechanic replaced the hose, 8 coil pack boots and 8 spark plugs and the idle is a lot better. Thanks for the advise on here and I hope that this takes care of it.