I own an 2011 Audi A4 2.0t 8HP-55a with 100,300 miles and I need help knowing what is the cause of this issue. I have began seeing an oil leak on the front driver side near where the oil filter and the dipstick sits at. The leak seems to be a type of spray (seeing dots of oil on oil filter, coolant expansion tank, throttle body hose and driver side plastic engine heat shield and idler pully. It started when I first began to get bad average gas mileage from 31mpg to 26mpg, at the same time also, I began noticing that the car needed .4-.5 qt of oil using aftermarket dipstick. Another thing I noticed while on the highway, I was applying moderate to heavy throttle and suddenly the engine seemed to stall for a complete second, this has only happened one time. This also started to happen when I added "Lucas oil deep clean fuel system cleaner" to the tank. I have always added a portion every oil change and the engine always responds with a temporary mpg boost.
I tried using common sense first seeing if it was a loose dipstick or a loose coil pack and upon inspecting the spark plugs, cylinder 1 plug was fouled and the bottom three lines of threads were covered in oil (sorry I didn't take a picture before cleaning them). I cleaned all 4 plugs out using ultrasonic and the engine was happy and snappy. I moved cylinder 1 spark plug to cylinder 4 and 100 miles later, that same plug fouled again but no oil. Threw old double plat plugs 15k mi. old out and put NGK-2267's, car seems happy and will check plugs in 50 miles. Upon inspecting from a top view of the engine (pics included) I see that there is a good amount of oil on the oil cooling lines but I'm not sure where that issue points to. Onto the engine color, brand and smell; Liqui-moly 5w-40 molygen green hue, engine oil has lived for 3000 miles on conditions that are 85% highway and 15% city, the color on a white paper towel is a golden honey and there no burnt smell. No leak on valve cover gasket.
Important factors that may contribute to this problem: Stage 1 tune was added 9,000 miles ago (more power= more stress on components) , aftermarket transmission mount (not oe), turbo muffler delete (not oe), custom air intake system (not oe). It could also be the weather (30-50 F morning startups).
This stuff may be a factor so, in the past 10,000 miles I have done a engine intake valve decarbonization, ultrasonic cleaned fuel injectors and replaced seals, 4 R8 coils, brake flush, transmission and filter flush, front, center, rear differential flush and steering fluid flush. I also do 4,000 to 5,000 mile oil interval changes.
I hooked the car up onto an Ancel OB2 VD700 and I don't get any fault codes upon scanning the entire system.
I am the second owner of this A4 and the previous owner seemed to do hefty work on this car. Vacuum pump replaced, water pump replaced, engine pistons and rings replaced, valve cover gasket replaced with Authorized Audi Dealership receipts.
I love this car to death since it's a balance of sporty, fuel efficient (was) and luxurious, I don't want to get rid of it and I'm not afraid to get my hands dirty, so if anyone could give their thoughts it would be greatly appreciated.
Imgur link to engine running: https://imgur.com/gallery/8A96hHd
Imgur link to engine oil leak: https://imgur.com/gallery/h6UJNYg
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