Hello all,

Thought I'd tap into the forum's collective wisdom to figure out a problem with my new-to-me Ford. It has a 4.6 V-8. I've had this vehicle for 2 months, and I've developed a vibration when sitting at idle. The vibration develops when the engine warms up, at cold start the engine runs very smoothly. The vibration seems to be more prevalent in gear, but is still noticable when in park or neutral. Acceleration is smooth, the vibration is only noticable when I have my foot on the brake, such as at a stoplight. Mileage is very good, better than I would have expected (19-20 mpg). No check engine light. The vibration doesn't seem to be causing a problem with performance. I have attempted to clean the injectors with Lucas and SeaFoam cleaners in the tank, with some success, but the vibration returns. The vehicle has 83,000 miles. Any ideas?

Commander

 

Welcome to the forums here at FTE. Since your truck has over 83,000 miles on it, I'd be curious about the spark plug condition. Even though the 4.6 has plug change intervals of every 100,000 miles, that is for normal driving conditions. Without looking back in the owners manual, I believe more severe use such as long idling and driving in dusting conditions and lots of towing lists plug changes at 60,000 mile intervals.

 

Thanks for the suggestion. Changing the plugs is definitely on the agenda in the near future.

Commander

 

Welcome to the site
lucky you have the 4.6 ,no plug change problem
sounds like your idel may be getting to low
is it below 700rpm in gear ,brake on?

 

Thanks for the welcome!

I don't know what the rpm is at idle or at brake, no tach. This is a pretty basic work truck. I'll have to have it checked, sure would be an easy fix! Doesn't seem like that, though. After reading other threads on this subject, others have had this trouble, too. I'll keep reading.

I'm going to be doing scheduled maintenance during the next couple of months, tranny flush, plug change, etc. If I hit on something, I'll let the group know.

Commander

 

try disconnecting the battery for awhile
maybe it will learn something new

 

couple of things.


1st off: I had the exact same issue with the 4.6 in my Mustang while I was living in Seattle. Ran like a champ when driving around, awesome MPG's...and plenty of power.


But at a stop, the motor ran "rough" when just idling. In gear or in park. That was with 91 Octane


I shipped it to Hawaii. Out here, we have 91/92 octane. I started using 92 octane and the rough idle almost disappeared completely. Might want to try a tank or 2 of 89 octane. It'll only cost a $1 or 2 more...see if it helps. If nothing, go back to 87.




2ndly: the 4.6 motor is a bit of a rough idler out of the box. a little bit of shaking is normal. It's a pretty common compalint among the Mustang crowd...and I've seen alot of posts about it on FTE as well


3rd: the 04 and early 2005 model trucks have a very restrictive PCM fuel map strategy. they run pretty lean straight out of the box. so, the truck may be borderline leaned out while idling...and that could also explain your good MPG's.



lastly: welcome to FTE. please stick around. we'll help you lighten up your wallet a bit. the modification of these trucks is pretty endless. you can go cheap to expensive...and have a very nice truck either way you choose

 

Thanks so much for all the replies!

Regarding the higher octane: after using the Lucas and Seafoam additives, I have been using mid-grade gas for the past couple of weeks, Shell gas specifically, and I think that the rough idle has improved. Still there, but less intense.

Kinda good to hear that this may not an isolated problem, if it tends to run a bit rough typically, I will rest easy.

I am very pleased with the performance of the truck overall. Not looking to do any mods to increase performance, as this is basically a work truck for me. But, its my baby now, and trying to treat her right.

Thanks again!!

Commander