Have Ford Questions? Ask a Mechanic for Answers ASAP
Do you have a check engine light on?
Can you hear any rattling noise from the engine that accompanies the rough idle?
We see this all of the time on our trucks. I have a fleet of about 1200 fords and 200 or so have the same engine as your truck.
The most common cause is worn variable timing solenoids. They adjust the engine timing based on engine temperature using oil pressure. Sometimes low oil pressure/low oil level causes them to act up, sometimes they are just worn out.
Usually when we replace them we end up replacing the cam phasers as well. Do you hope to fix this yourself?
Ford will likely push you to replace the engine. I hate to say it, but that is their typical response. They have a litany of tests that they will run to determine if it is worth replacing and if it scores low on just one of those tests they will condemn it.
I changed a timing set on one of these trucks as side work (I work for a government fleet) a month ago and I charged the customer $1500. He came to me because the dealership quoted him $7000.
If you haven't already, I would make sure it has good clean oil. That will give the solenoids and phasers the best shot at working correctly since they operate using oil pressure.
You might also consider replacing just the phaser solenoids and seeing if that improves the symptoms. They are a pain on the 2008 since you have to remove the valve covers, but you can get the solenoids for about $100 for a pair. If you are fairly mechanically inclined you may be able to tackle this one yourself.
If you continue driving it with the problem the worst that will happen is the timing chain and chain guides will wear out and need to be replaced also. That's what the customer I had did- he ignored it hoping it would go away so I had to change the whole timing set. Not a terrible way to go since most of the timing set is work out and could use replacement at 120k miles anyways. If it was my vehicle, I'd probably keep driving until it got worse or I found a good deal on a used low mileage engine.
Did you need any additional help with your vehicle? Please don't forge to rate if I have been of some assistance.