Ford Repair: 1998 ford explorer 4wd SOHC..., ford explorer 4wd, upper intake manifold

Question
1998 ford explorer 4wd SOHC 126,000
check engine light is on po171 system to lean bank 1 and 2,4,5 misfiring
I have changed the pcv valve and hoses and the lower and upper intake manifold o rings.
For what I have read on po171 error message it usually mean a vacuum leak. After changing these things I still hear a leak buy the pcv valve area.
What is the best way to check for a vacuum leak?
IF i find the vacuum leak and repair it do you think the misfires will stop.
Are there are other problems out the with he explorer that are known to cause this issue

Thank you for your help

steve

Answer
What I would do first is reset the check engine lite by removing the neg battery cable for 5 minutes, then recconnect. Then go to the parts store and buy a can of leak detector, spray this on all your vacume lines, and the leak will show up. Make sure the engine is running, this should fix this issue.. TY..