It would help if you knew or remembered the exact diagnostic code read, for ex. P0102

Then you could go here and the cause and possible solutions would be shown.

 

first reset the code and see if it comes back before you worry

 

lean means more power!! lol

 

Start by checking the engine for vacuum leaks.

 

^^ I just dealt with this problem a couple of months ago. You most likely have a vacuum leak. The number one point where the leak tends to happen is the PCV hose that goes into the intake. The rubber in the hose breaks down over time and forms a hole at the elbow. Check out this thread and see if it helps: http://www.focusfanatics.com/forum/showthread.php?t=28249

 

[headbang]i think that you should check that (vacuum lines) good advise.

 

defiantly check for vacuum leaks. most common concern of lean codes.

 

I reset and the CEL came on again at 100 miles.

 

There ya go. The PCV line seems to be a common culprit, but that usually leads to low idle before CEL's. I'd still investigate that one first by removing it, and folding the rubber pieces to expose cracks.

 

check that damn vacuum line for the intake at the back of the engine. I am doing this repair tomorrow. http://www.focusfanatics.com/forum/showthread.php?t=28249&highlight=vacum+line