I recently bought a 2006 that idles rough, not real bad, but bad enough for me (and my 9 year old kid!) to notice. I asked the dealer where I bought it and they put it on the computer and said everything checked out. He siad "it's a characteristic of this motor." I've never heard of such a thing. The truck has 27,000 miles on it and the dealer flushed the fuel system. He said the throttle plate had a lot of carbon on it, but it still idles rough. Anyone have any suggestions. Anyone else's 4.6 idle rough?

Ed

 

Ed, yeah the 4.6 has a slight vibration at idle but nothing that should stand out. Could be fuel filter even though they flushed the system. A couple other things that come to mind are the coils on plugs or the injectors but those are just guesses. Seems to me too that it would have thrown a code. How does it run in drive at idle or low rpm? any hesitation or shaking? Others here will be able to help you more on this. I had a similar issue with mine and it turned out to be one of the coils had popped off the plug.

Eric

 

If the engine is not running rough but seems like a vibration at idle check the oil level. I have had trucks (4.6) with too much oil in the crank case produce a vibration because the crank is slaping the oil.

 

The little shake you feel is its nature. I thought the same thing when I 1st got mine.
I check a three others on our lot and they were the same way. I guess I just never noticed it over the years till I actually owned a 4.6.

 

sorry to buck the trend but all the 4.6 work trucks (2005x2, 2006 and 2004) we have plus my personal 2005 4.6 doesn't have a rough idle...now I know that with the drive by wire we don't have an IAC I am guessing. So to go back to the obvious, flushing the fuel system doesn't touch the filter...change that first. Check your air filter. Do you run a tuner? Mebbe you tweaked the timing wrong if you do? Did the dealer clean the throttle plate? Did you check the work they did? Nowadays I generally don't trust even the dealer...ESPECIALLY the dealer...

Another good point brought up...make sure all the retaining screws are present on the COPs. A coil might have popped up.

D

 

@db_tanker.
What do you consider a rough idle?

I checked all the way down to an 05 and it had the same slight shake at idle as my 08. I wouldn't consider it rough, just not silky smooth.

 

my mother and father in law both have Grand Marquis...different year models...both have 4.6 engines and idle fine. my wife's Escape with a 3.0 has a smooth idle. no stumbling and no vibrations.

In fact I just went outside to make sure...started my pickup and waited...while cold I felt one or two...not quite stumbles but just a RPM variance in my seat...otherwise after it idled down, in park, there was absolutely no stumble...RPM was steady from 750-760 RPM.

In comparison to my vehicle, and my experience with other of the like, you have a problem. Mebbe in need of a tune-up, I dunno. But with 94000+ miles my truck doesn't do what the OP says his does...

 

Thank you all for the responses. "Rough" may be a bit strong to describe what the truck does. Small, but noticable, vibration when idling in drive is probably more accurate. I had a 96' 150 and it purred very quietly. So, maybe I'm just used to my old truck.
Having said that, there is an issue that I'm trying to figure out. Shortly after I bought the truck it stalled as I neared a stop. I took it back and they replicated the problem, though it didn't stall--the rpms dropped to 490. Even after they flushed the fuel system and said the throttle plate had a lot of carbon build-up, the engine noticably labors as it shifts into low gear. It doesn't feel like a tranny problem, it feels more like something in the engine. The odd thing is it doesn't throw any codes, even when it stalled. I'm going to take it back and see if they can solve the problem.

Ed

 

again...with no codes, I am pointing to the fuel system...primarily the filter.

might be an issue with an injector as well...

 

My '06 4.6L is smooth at 60K+.

 

My suggestion would be a coil getting weak.

 

You may want to take your butterfly off and clean it yourself with carb cleaner its not hard. I would also spray out the intake because its probably gummed up. My engine shakes a bit but idles steadily around 700 in park and drive. I am going to change the plugs in it soon to see if it helps.

 

I owned an 05 with the 4.6 for nearly 5 years. From day one this truck vibrated at idle. Changed plugs, cleaned throttle body had codes pulled and nothing. Drove me nuts. Didn't run bad and wasn't rough, just a vibration at idle, and vibration is actually putting it a bit strong, it wasn't bad but was noticeable. Almost like a white noise.

 

Re-looking this thread and I would recommend cleaning the throttle body and MAF sensors with approriate cleaners. Should help.