2000 Widstar mis-fire on cylinder 5 and tapping sound

Yesterday my 2000 windstar suddenly begin running rough and making a tapping sound. I thought it had fouled a plug and figured it was time to to the valve cover fix anyway. I did the complete valve cover fix today and replaced the spark plugs. A couple of the plugs looked rather bad so I thought I was on the right track. When I started the van after all the work today I still have the extremly rough idle and tapping sound. It sounds like a timing knock. I am thinking it may caused from some carbon build up on the valves? I took it to a local part store and it read mis-fire on cylinder 5. I hooked up the old timing light to cylinder 5 and it seemed to be getting fire. This thing is making me crazy any and all input would be appreciated.:banghead:

If it sounds like a hollow knocking the upper intake manifold may have come apart inside (It's a 2 piece design). My '01 did that and it scared the crap outta me until I read that the internal baffle may loosen up a bit and cause a knocking sound. I found a new updated manifold on eBay for $50 and that solved the problem.

Thanks for the input but the upper intake manifold was still intack when I took it apart to replace the isolator bolts. I could see some carbon build up on the valves but I honestly did not look real close at cylinder 5. Unless someone wants to jump in with an idea I guess I will take the intake back off and take a close look at the top of the valves on that cylinder.

Please offer any thoughts possible. I need to get the wife's van running so I can get back to deer hunting.

I have not seen posts on it....but a fuel injector can make a noise also.
Though not common on the windstar, it could happen.

A cheap thing to try would be some Berryman's B-12 Chemtool in the gas tank to clean the fuel system....and the injectors along with it.

I like to rule out the cheap and easy first.......and.....even if it is not the cause.....it is a good thing to do now and then anyhow.

The other thing to check is whether you are getting spark at cylinder #5.
That could be an issue with the spark plug wire, coil pack, or even the spark plug (even though it's new).

If you are old enough, and have old clutter around.....a timing light would be a easy way to check for spark on that cylinder (it is on the front of the engine....middle cylinder).
If you are not old enough.....you are wondering "what's a timing light", and you most likely don't have one, although a friend might.

Thanks to everyone for your input. Sometimes the problem is right in front of my face and I can not see it. I found a broken valve spring on cylinder 5. Replaced the spring and the old jewell started right up nice and quiet. One slight scare was a rough idle. After standing around with the neighbor listening to it for a while he commented that it almost sounded like a vacuum leak. Duh, I had just had several vacuum lines off working on the little valve cover, isolator bolt probem. Took about 2 minutes to find a line off. Idle went smooth and is running fine now.

Sometimes I get so hung up looking for electronic and computer problems that I forget to check the basic motor stuff that I grew up working on.