It's worth checking the torque on your intake manifold too. Might not be a gasket, just loose.

 

Hey, Those are lean fuel codes, if you checked for vacuum leaks and found nothing, I would check fuel pressure at engine. Low fuel pressure can cause lean codes, which can also cause spark knock(pinging) that you are hearing.

 

Listen I have the same problem with my 97 F150 with 120,000 miles on it. I have replaced the PVC Valve checked all the vacum lines and even went as far as replacing all the O2 sensors and monitors. That did not fix the problem and with looking around this forum there are multipule things that could could cause this condition. So I have decided to have Ford tell me what is wrong with it. I will let you all know tomorrow when I find out what is wrong with my truck.

 

Okay I am back like promised. The fix for my truck was a PVC tube and cleaned the MAF sensor. Good luck with your repairs.

 

I said that on page one lol


CLEAN THE MAF or VAC leak(PCV) was said as well ( :

Most common cause of codes - the original poster of this prob had already did this - read

 

02 screw with 82k. It started acting "funny" a few days ago and set the 171, 174 codes. After searching the the forums I started checking things - turned out to be the PCV elbow behind the TB/intake elbow, PITA to get off and on!!! (probably shoulda just taken the TB and elbow off and cleaned it anyway - but was pressed for time) It was all soft at the curve with a hole in it. Discovered it by spraying carb cleaner around all the fittings - when I sprayed back in there the idle would rev a hundred or so - almost a bit hard to tell since the idle had gotton so erratic anyway from the leak. I had to use 2 feet of 5/8 heater hose (no one had the elbow at 8 p). Guess I'll look for the corrrect part tomorrow - the hose wasn't quite snug enough.