![]() The engine control module (ECM) calculates the amount of air going into the engine through the positive crankcase ventilation (PCV) system. This means that unmetered air is entering the engine without the engine sensing it going through the mass air flow sensor and throttle body. P2279 is an OBD-II generic code for the engine control module (ECM) detecting a vacuum leak into the engine. Your long term trim should show a figure over 20% outside of range indicating an adaptation made to correct the vacuum leak, providing no fault codes have been cleared recently.Intake Air System Leak What the P2279 code means Watch the idle value change in the short term trim when you remove the dipstick as this creates a vacuum leak. If you have access to VCDS, with the engine running and upto temperature (so it’s not running in closed loop), look at measuring blocks 032 and 033 for LTFT and STFT. The issues under load are less likely to be vacuum related as vac leaks are only really apparent at idle, so these are more likely to be linked to your misfire issues. What I’m saying here is given your pre existing lean fault, you may have a leak on the dipstick which once outside of the ECUs parameters is creating a fault code and the poor idle. The ECU can only make alterations upto around 20% plus or minus, in order to effectively achieve Stoichiometry, or lambda. These vac leaks are adapted by the ECU overtime (evident in the long term and short term fuel trims LTFT / STFT). Similarly, if either aren’t sealing or leaking slightly this will also create a vacuum leak. Removing the dipstick or oil filler cap creates a vacuum leak. Thanks in advnace and sorry for the long post Īside from that i get a better fuel mileage and the issue mentioned above with the misfires has been solved, another thing i noticed which im not sure if it was before is when im removing the oil cap, a white smoke comes out from there, is that normal ? ![]() Now after the replacement when pulling the dipstick out the idle stays completely the same, correct me if im wrong but this means that the PCV is faulty, if I'm removing the oil cap the engine will go rough until i seal it back. Just for the heck of it i checked the symptoms again and that's why i think something is strange. I ordered a PCV valve from amazon 06H-103-495-AH and replaced it with my pcv 06H-103-495-A that came out of the factory, and the next morning the issue disappeared! YAY! įrom what i saw on the web this is indicating a failure on the PCV ,i also could hear a small whistling noise on those cold starts coming from the little hole on the pcv itself which is also indicating a failure. i had a suction and a pop sound and the engine went really rough when i removed them. I checked the pcv by removing the oil cap and dipstick (not at the same time) when the engine was running. The next morning i used OBDELEVEN to check misfire and it did a cycle of 130 misfires most of them came from Cylinder num 4 then 1, cylinder 2 and 3 were pretty ok.Īfter searching the web i came across PCV valve failure symptoms, i had most of them. So I started diagnosing the issue from that. I didn't have any check engine light but on one of those cold mornings, I had a fault code detected with OBDELEVEN =P0171 SYSTEM TO LEAN. RPM was normal, but when trying to rev up a little bit the rpm would go up and down (i have a video if that would help). the rough idle disappeared after the temp gauge started to move a bit and that's it , ![]() ![]() Two weeks ago I started having rough idle only on cold morning start ups. I have an Audi 2008 A3 2.0T with 107,000 km on the clock. I'm a little bit confused about an issue I was having,
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