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Billy
Billy, Trainer/ Master Technician
Category: Audi
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Experience:  Trainer 8+ years, master tech. 10+ years, SAE member
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Audi: 2002 Audi A4 Avant 3.0 Automatic. Had problems with a

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2002 Audi A4 Avant 3.0 Automatic. Had problems with a bunch of codes coming up like o2 sensors, MAF, misfires etc. Turned out to be Cranckcase ventilator valve. replaced it and things are better. However, while the car is running, I take the oil cap off and it has a lot of suction to it when pulling it off and alos engine runs erratically when I do this. Is this normal?

Billy :

Hello and Welcome! I'm Billy and i will assist you with your inquiry. Feel free to ask if any further info is needed.

Billy :

At idle, and since you have the oil vapor hose from the valve cover to the intake manifold, you will get suction from the oil cap.

Billy :

And when the oil cap is removed, excess air gets to the intake manifold (without being counted by the MAF), so you have a lean mixture, causing the erratic idle.

Billy :

In short, yes this is normal.

Billy :

Thank you for your trust! Get back to me if you need more info...Thank you in advance for the positive rating...
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Billy :

Regards, Billy.

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