CEL light flashing-shuddering when idle. 03 passat 1.8 Turbo. Thinking its an air leak somewhere? Can hear air but can't figure out where its coming from...

all 4 coils have been replaced in the last few months. When the car drives its fine, but when idleing it sputters and acts as if there is a vacuum leak or something. Acts as if it wants to stall out. Had a code reader put on it tonight and it said something about a fuel loop? can't really remember what my fiance said exactly. The guy at the auto parts store said gas cap. Will a faulty gas cap really cause this much trouble? all 4 coils have been replaced in the last few months. When the car drives its fine, but when idleing it sputters and acts as if there is a vacuum leak or something. Acts as if it wants to stall out. Had a code reader put on it tonight and it said something about a fuel loop? can't really remember what my fiance said exactly. The guy at the auto parts store said gas cap. Will a faulty gas cap really cause this much trouble?

It's definitely not the gas cap. While that will cause a cel, it will not make it flash or run rough. There are some black rubber breather hoses that come off of the valve cover that tend to rot and crack, you should be able to feel that they are very soft or broken by touch. There is also a black plastic tube, I'm not positive that it was still installed in 2003 though, that comes off a valve under the intake manifold and goes back in just under the throttle body. It can be seen by looking straight down next to the throttle body, and you can get your hand on it by removing the 3 screws that hold down the coolant resevoir and lifting it out of it's place after disconnecting the wiring underneath. It should be firm, not soft. Sometimes they develop a break along the length of the tube. If you could get me the exact codes from the code reader it would be helpful. It's definitely not the gas cap. While that will cause a cel, it will not make it flash or run rough. There are some black rubber breather hoses that come off of the valve cover that tend to rot and crack, you should be able to feel that they are very soft or broken by touch. There is also a black plastic tube, I'm not positive that it was still installed in 2003 though, that comes off a valve under the intake manifold and goes back in just under the throttle body. It can be seen by looking straight down next to the throttle body, and you can get your hand on it by removing the 3 screws that hold down the coolant resevoir and lifting it out of it's place after disconnecting the wiring underneath. It should be firm, not soft. Sometimes they develop a break along the length of the tube. If you could get me the exact codes from the code reader it would be helpful.