Engine code p4011

SOURCE: 1997 lincoln town car check engine light-P0402 code

did you replace the egr valve

SOURCE: Car coded yesterday p0303 noe check engine light flashing

The only thing left is the injector or a vacuum leak on the manifold gasket sucking air in and causing a lean condition. Thats is its the only common issue providing you dont have a head gasket issue leaking coolant on that cylinder and the compression and valves are not leaking. The old spark plug should show a coolant issue if present. The white part will be shiney if you have a coolant loss. If the coolant is looking real dark you should have the cooling system checked for gas being pushed into the cooling system on compression stroke thru the head gasket.

SOURCE: bought car and was overfull on oil, oil light and check engine on

what kind of car? have you looked up the code? need more info

SOURCE: I just bought this car

Tighten up the gas cap.Since it came on right after you put gas in your car this is most likely what it is.After a number of cycles of the key the light should go out on its own.(Don't remember the number of times you have to cycle the key)

SOURCE: Check engine light has been on since we bought the

No need to guess. Take the vehicle to one of the Major auto parts stores like Auto Zone and ask them to connect their scanner to it and identify the fault code. That will tell you what needs to be replaced. As far as dust getting into a sensor, that's a new one and original. Definitely find another shop to work on your vehicle in the future as it doesn't sound like those guys know what a wrench is.