Knock or Pinging Noise

I have a weird Knock or pinging noise that seams to occur sometimes. I got the Check engine Light on with Error codes 0171 and 0174 Too lean message. I have replaced Spark Plugs and Sensors I've reset the computer a few times but error still comes back. I changed my Air Filter and I check my MAF and the MAF looks like its new and not dirty. I'm not too good on finding vacum hoses so I'm not sure where to find all of them. but What else should I end up tryin gto fix these problems. I don't have a lot of money so I can't afford to take this car to the shop. Oh the miles is 99k on a 1999 Windstar.

Click this link for all the info. you need. Good luck!
http://www.automotiveforums.com/vbulletin/showthread.php?t=338113

Thank you. I think this does sound like my problem. I'll start calling the ford dealer today and maybe I can get these parts to do this. Also is these job very diffcult. I've done some things on my other cars like I did replace the clutch in my Toyota and a few other things. I don't usualy mess with the heads because there is alot of things to take off and put back. but maybe I'm just parnoid. I think the directions on this seam not too hard.

The upper intake manifold repair is far easier than replacing a clutch. The combustion heads are not involved in the repair ... all plastic parts.

Another link that may help you is this one for a 2000 windstar....but should be very similar to your '99.

Nice step by step instructions, complete with clear pictures, and part numbers.

http://leckemby.net/windstar/windstar01.html