Car Stalls when I remove the oil filler cap

[baldrick123]

Hi All

I have a A4 cab 55 plate 2.0 litre fsi. I removed the oil filler cap whilst the engine was running and the car stalled. I tried again and the engine was drawing in lots of air through the oil filler cap and again stalled when it is completely removed. I wondered if this was right!


Thanks

Andy

[zollaf]

do you have any other problems that would suggest that this would be a problem ? does the car run ok, no smoke, no loss of power, no rattles bangs or clanks ? i suspect not. the breather system is connected to the engine. removing the oil filler cap opens a free channel of un metered air into the inlet, thus confusing the ecu. not a problem so don't worry, just don't try to drive with a missing oil filler cap, which is something you can't do, ooh, do you think they did it on purpose to stop people forgetting to replace their oil filler cap ?

[Doctle Odd]

You shouldn't remove the oil filler cap with the engine running anyway some cars can give you a scalding oil facial...

[darich]

I've accidentally not tightened mine properly and the car runs like a bag of bolts....doesn't stall though.
Mine has no problems at all (touch wood) so I guessed it was something to do with altered pressure in the engine.

[Stuart Piper]

i would have thought that the cam cover would have been under some vacum to recirculate the oil via a breather system? I am sure someone more technical will confirm this, but it does not sound like anything to worry about. With the vast amount of emission regulations on cars, i would have thought that the cam cover would be monitored or at least under some vacum.

[Steve220]

You're letting into the system bypassing the maf sensor, ecu gets confused, runs lean, stalls.

[steveheather]

Hi there. You have described air rushing into the engine when via the filler hole when you remove the cap. Based on this single symptom only, it is POSSIBLE that you may have a faulty crankcase breather valve.

This is a problem that crops up frequently on many VAG cars and is sometimes difficult to diagnose. Well described in this forum thread - Crankcase Breather Valve Location

I don't have knowledge of the 2.0 fsi but imagine that it's not too dissimilar to the 1.8t in the featured thread. It is possible to have a faulty crankcase breather valve without fault codes showing (from experience).

A simpler test with the engine idling and the oil fillercap in place is to gently try and remove the dipstick. If it shows resistance and gets sucked back, then the crankcase breather valve is a a good starter at minimal expense (about £8 from TPS).

Post #2 in the thread suggests clamping a pipe to test. See if you can locate this pipe (or equivalent) on your 2.0 fsi and simply pinch it between finger and thumb. If you get the suggested result, then you have found your fault.

Steve