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That plastic tube only lets air into the box to cool the ECU, should not cause P0171. P0171 is system too lean. You should trouble shoot and isolate faults from the simple to the more complex and more expensive fixes:

Most cases P0171 is caused by leaks in intake air, could be unplugged or leaky air hoses between the air box and the throttle body. Check to make sure all little black hoses are plugged in at the right ports and not leaky or damaged.

To find hose leaks, You can idle the car and spray soapy water on the hoses. If the engine revs faster, that area has leaks.

Check the air filter, make sure it's nice, clean, not dirty or plugged up, is assembled properly, all seals are tight, not leaky. If not it will let too much air into the system causing lean condition.

P 0171 could possibly be caused by defective O2 sensor 1, which measures oxygen level therefore air/ fuel mixture in the exhaust. If it sees high oxygen and low fuel ratio it will think there is too much air and not enough fuel therefor too lean.

It cold be caused by dirty fuel injectors not injecting the right amounts of fuel. Engine would sputter at idle and wide open throttle.
 
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