I have a 2003 Ford Expedition which is having some rough idle issues. The vehicle sat for several months and was not driven. When we went to use it, it had a very rough idle, gas smelled bad, sputtering etc. The engine light came on and we took it in and it said it was misfiring on cylinder 1. We had recently replaced ALL 8 coil packs because the one on cylinder 1 was misfiring. Thinking it was the coil packs again, we used on of the old ones that we had taken off that did not register being bad and put it on. The symptoms did not go away. he tried another one of the older coil packs and still nothing. Then, we replaced the spark plugs. The vehicle didn't have much gas in it when it was sitting, but we used all the old until it was VERY empty until refilling and then treated the gas with Seafoam. At this point, the vehicle still has a rough idle while sitting in park. When you put it in drive, the rough idle gets worse. It will stumble about three times, and then rev up. After it revs, the rough idle settles into a normal idle for about 3 seconds and then goes back to the rough idle. While driving the vehicle, the check engine light comes on driving down the highway at about 55 mph, but then goes out when you stop and slow down to about 20 mph. Any suggestions? Could this still be coil pack? or something else?

 

Clean the IAC and replace the fuel filter since it sat for so long.

https://www.ford-trucks.com/forums/9...4l-triton.html

 

Replaced #1 injector the other day to solve this issue on an '08.