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Did a tune up on my car today.

3rd spark plug hole had oil in it and the spark plug tube was raised about 1/4 inch. I knocked the tube back down with a socket and hammer and cleaned up the spark plug wire and the tube the best I could and then replaced all the plugs.

Since like december I have been getting really shitty gas mileage, people told me that it was just the winter grade of gas, since this was my first winter driving I figured it was the gas too. Could oil in one of the spark plug holes be an underlying cause of bad gas mileage?

And what would cause the tube to come up? Is knocking the tube back down a sufficient fix or will I have to change some seals or something?

And my car is also throwing a code:
P1494(M) Leak Detection Pump Switch or Mechanical Fault Incorrect input state detected for the Leak Detection Pump (LDP) pressure switch.

Anyone know what this is? Could this be a cause for bad gas mileage?

Any help will be appreciated. Thanks

The FSM recommendation for the spark plug tube is to replace it: Clean the bore put loctite on it and press it in place I just reused mine cleaned with brake clean scuffed up the surfaces and red loctited, they're still in there. The leak detection thing could just be a loose gas cap/bad cap, or a leak in the line to the tank. The pump pulls a vacuum on the fuel system so no fumes escape to the enviroment.

how complicated is replacing the spark plug tube?

and what causes the tube to pop up?

and the LDP could be a leak in the fuel system somewhere? Possibly why im getting bad gas mileage?

The tube isn't too bad to do, you will have to remove the valve cover and pull the tube. I would leave the spark plug in and soak the tube bore with brake kleen, soak it up with paper towels a couple of times to get the oil off the surface. you will have to soak up the oil surrounding the area to keep it from running back in.
There could be a problem with the sensor on your leak detection pump system. I'm not sure where the parts are located I think in the rear right wheel area, and under the brake booster (there is a plastic tube that runs near the PDC/battery down below the brake booster, I think that feeds vacuum to the leak detection system). As far as the fuel mileage, I don't think that it is the cause, but I could be wrong. The plug wire could still be bad, having soaked in oil, possibly leaking enough spark to give poor combustion, but good enough to keep from setting a misfire code. Or the o2 sensor is getting tired. The leak detection is only to check that the fuel tank has a vacuum on it so fumes aren't escaping. If there isn't the proper level of vacuum it sets a CEL. Like if the filler cap was left off it can't pull a vacuum. But from the way the fault code reads I don't think thats it. Possibly snow/ice built up in the rear and pulled a wire loose.