Elantra MD (2010-15) :: Check Engine Light Comes On And Off

I just bought a used 2011 Elantra GLS and am having some issues that the dealer cant resolve. What is happening is the the Check Engine light comes on and off. It will be on for a day or so, then go off for a day or so, so I am thinking its the gas cap. So I tighten that thing up as good as I can and pulled the negative battery terminal and problem solved. About 2 days later, and about 200 miles later on the same tank of gas, the light pops back on. So I call the dealer and took it there the next day.

On my way to the dealer, the light goes out. They try and pull the code, but the ECU is showing nothing. I asked if the ECU stores codes and I was told that when the light goes out on its own it clears the ECU of the code. Not sure if that is true, but that is what I was told. So I drive the car home. I fill the car with gas, drive about 100 miles and the light comes on. I call the dealer the same day, take it over, and on the way like the car knows it goes off and guess what? Dealer cant do nothing.

Now to make a long story longer, this is what I know. The car is not a CA car. It was sold in GA and was a prior rental. It ended up in CA and was sold as a certified pre owned from a Hyundai Dealer, I actually bought the car from a Mitsubishi Dealer and they dealer traded for this car (thats another long story) the carfax does show that it failed emissions but passed after several attempts. Which I thought was odd on a ULEV vehicle. Since I liked the car so much and the price was good, I bought it since it did pass smog eventually.

Once I get the car home, I do my usual thorough look. I clean everything to my standards. I am cleaning the engine compartment and took the engine cover off. 1st thing I noticed was the Spark Plug Coil Packs all the 10mm bolts that hold them in were loose and 2 of them were completely off!! So I decided thats odd, so I pulled the plugs out and they were the NGK's so just in case I put a brand new set of the NGK laser Iridiums back in and tighten everything up. Then I notice where the PCV valve is on the valve cover, the hose that goes to that to the intake tube does not look stock. The hose looks like fuel line hose that someone put on it and the clamps are not stock. So I am canvasing for OEM replacements of those parts now. Then when I was installing the mud guards, on the drivers side rear tire where the gas filler tube is I notice another non OEM clamp. So someone was messing with this area of the car too.

The car is averaging 26-28mpg's in the city and I have been getting 35-37mpg's highway so I don't think there is anything major wrong here. I believe that either the PCV valve hose is kinked and may be causing a fault, or that since it was a prior rental that people were over filling the gas tank and maybe blew the expansion valve in the gas tank, causing the fault. I have no way to prove this since the light goes on and off and clears the ECU every time I take it in.