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Q: I keep getting OBD-II codes P0171 and P0174

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I keep getting the P0171 and P0174 lean bank 1 and 2 code. When I fogged the intake the only smoke came from the press cap on the idle air control valve, I did this on my 02 F-150 with a 5.4 no smoke. When I say press cap I mean the cap on he valve that looks like a freeze plug crimped over the valve. Is this normal, since taping around the valve I haven't had the check engine light for over 300 miles.

My car has 203500 miles.
My car has an automatic transmission.

A: Since you have codes that both banks are le...

Since you have codes that both banks are lean then the problem will most likely be from air entering the intake manifold after the mass air sensor. The idle air control valve should not have any air leaks from the valve and may be contributing to the codes you are getting. It would be recommended to scan the computer data to see if the mass air sensor is registering the correct barometric pressure reading. This reading should show the proper pressure for the altitude your vehicle is at. If the data is reading that you are above more than 1000 feet more than what you are at then the mass air sensor is causing the codes and the mass air sensor needs replaced. The mass air sensor can be damaged by an air filter that is the oil bath type and should be the dry type filter. Replace the air filter if it is incorrect type or is dirty restricting air flow into the engine.

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