nibhelim

Hi there, I got a a4 2005 1.8T with 120k, since few months the gas consumption went way up and the car is not responsive as it used to be. (it used to consume a lot of oil, 1 bottle every 1500miles, while now is barely consuming any oil)

VAG errors:
17736 knock-control cylinder4 exceeded value of resistance too small
17733 knock-control cylinder1 exceeded value of resistance too small
16684 random/multiple cylinder misfires detected short circuit to another valve
16688 cylinder4 misfires detected short circuit to another valve
16840 EVAP system, very small leak detected value of resistance too low

any suggestions?

John535is

vacuum leak and PCV fail.

One of my sons had the same. Start checking all the black hoses for leaks, cracks etc. We found the crankcase breather (yes the one under the inlet manifold in about the hardest part to see) had gone brittle with age and leaked. Its kind of a hard plastic, be careful ours just broke apart and you don't want the plastic dropping down the hole into the crankcase where it can block the oil pickup.
That breather hose goes to a T piece, and theres a small PCV or non return valve which could explain your oil use if its failed.

nibhelim

thanks for the answer John,
I recently changed the whole vacuum hoses are you referring to number 6 in this picture? http://www.a4mods.com/pics/intakemanifold/IMG_1613.JPG
how did you checked for leaks? engine running and trying to see if there is any leak or is there some tricks to follow?

btw the car was consuming a lot of oil before, now is not consuming oil AT ALL.... is this what you experienced as well?
thanks again!

John535is

yes - follow 6, from memory there is a T section, it then goes to the crankcase under the inlet manifold (which was the pipe that was leaking) and there is a valve either in the T piece or immediately next to it.
I chased the leak for ages, in the end I purchased a plastic cap, drilled a hole and installed a fitting to my air compressor, installed the cap in the inlet pipe and applied about 10-15 PSI. This essentially pressurises the entire system, then checked for leaks. You get some leakage back through the oil cap etc but the crack in the crankcase pipe become evident and there was no way you could see it otherwise. I found the process on a youtube video so I cant take credit