Last week I changed the intake manifold on my 2000 F150 5.4L triton, I did it myself. Seemed pretty straight forward and I put everything back together the right way, so I thought... Anyways, after I put everything together and drove the truck for the first time I noticed it has a heavy vibration uphill and a slight vibration while in drive stopped with my foot on the brake, but not in park. I have no idea where to start looking for a resolution so if anyone has any reccomendations I'd much appreciate it!

 

That sounds like a spark plug or COP issue. Did you put new ones in? Did you use dielectric grease in the COP boots and make sure they are all fully seated on the plugs? Are all the COP connectors properly connected?

 

any codes? how many miles on it? Make sure all your vacuum lines are hooked up too.

 

It does sound like a vacuum leak....

 

In the process of changing the manifold did water get in the spark plug holes? Do you have a cel? I was involved in a manifold change recently I paid a friend to to it for a friend and when it was all said and done I had to dry out a couple of spark plug holes. Antifreeze get in them when the manifold comes off and drying the holes and plugs should get done in the process.