codes problem shooting on 2005 Ford Five Hundred

i got codes for p0109 p0191 p0171 they all point to something with the air intake what would be the first thing to check?

5 answers
the large hose from the air filter to the intake has a couple of small hoses that come out from it. make sure they are all secure and tight. the 171 is a vaccum leak code for trims.
check air filter first then mass air flow sensor
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i got code po193
were is the air intake at