2008 F150 4.6l rough idle when warm!!
 

Hey I am new to the forum and just purchased my first truck. I got a 2008 F150 4.6l xlt. The truck had 76,000km on it. I recently noticed that once the truck was warm the truck would idle rough at a light. The truck has never stalled and there is no diesel sound or ticking from the engine or timing components(also no check engine light). I have already cleaned the throttle body, changed the air filter and cleaned the MAF sensor but it hasn’t solved the problem. The truck did have a misfire and it was under the initial warranty so the dealership changed the faulty plug and COP. However I am not sure if my problem is coming from neeeding new plugs or if I should be testing my oil pressure? I have done a lot of research on this issue but being on a tight budget ( starting a business) I am trying to do as much and I can on my own. I hope someone can give me some help!!!! Thanks

You have a 4.6 2 valve, which does not have variable cam timing. I would change all the plugs and go from there. Put some Techron in the gas to clean the injectors.

The 4.6 2 valve doesn't have VCT.

The 4.2l V6 is OHV, just like old school engines...

Nope, the 4.2 is a V6 with OHV. 4.6 is a V8 with OHC.

Denso cops seem to be the recommended brand. They supposedly make the Motorcraft cops.

VCT = variable cam timing............

No. No. No. The 2V engines have plugs that are easily removed after you get to them. They are hard to get to. The 2V V8s have only 4 or 5 threads in the spark plug hole and you have to torque the plugs to 28 ft. lbs. in order for them to stay in place and not blow out. Spark plug blowout is an occasional problem with 2V engines. The manual says 13 ft. lbs. torque. Ignore that and torque to 28 ft. lbs.

It's been several years but I got labor estimates from a couplde of Ford dealers in the Miami area for changing spark plugs and they were $240 and $220. They charged $10 each for spark plugs. I ended up buying the same Motorcraft plugs from Advance Auto Parts for $2.79 each and I changed them myself. I worked very slowly and it took a while but I had no real issues.

Why, I'm embarrassed... I misread the OP's post. Sorry.

Your engine is the 2 valve version of the 4.6 engine that makes 248HP. It does not have a VCT system so there won't be any sensors. The heads starting with year model 2004 were redesigned so that you won't have the short threads in the soft aluminum heads. The spark plug change is like most any other engine. You'll remove the COP first. As I recall, it takes a 6mm socket to remove it. You'll have to pull and twist to get the COP to turn loose of the plug but it will come out. Then all you'll need is a long extension and a flex joint to remove all of the plugs. The plugs are about 4" deep in the heads. Since this will be your first time, I'd allow 4 hours for the change. Most of that is learning what is there and how to deal with it. You'll install the new Motorcraft ONLY plugs back in the engine and tighten them like any other plug. You will need Di-electric grease to use inside the tube of the COP. The grease is to seal out any water that should fall into the hole where the plug is at. I'd suggest using a generous amount at the end of the COP so that when it slips over the plug, there's plenty to be applied to the porcelain part of the plug. You'll install the COP simply by reinserting it straight into the plug hole. Make sure that you feel the COP snap onto the plug, there is a spring inside that goes over the end of the plug. Using care not to cross thread, reattach the COP with the 6MM screw that you removed. Yer done.

If changing COPs, I'd use Motorcraft only. These engines are extremely finicky about the parts used. Even a simple thing like a non Motorcraft PCV can be a major headache with random misses. The COP just unclips and is a real simple job. Might look at Rockauto for pricing. Here's what the COPs look like, obviously NOT Motorcraft though:
https://shop.advanceautoparts.com/wc...8_pri_larg.jpg