Engine suddenly hisses and nearly dies when idling cold

[owheel]

Hello everyone,

So my car has started doing something wierd when idling from cold:
- Car starts at 1100rpm with no issues like normal
- Revs drop to 850ish after 20 seconds or so
- Engine intermittently emits a hiss like a blow off valve
- Engine sputters and revs nearly die
- Engine management then corrects this and the engine surges to around 1200rpm and then returns to idling normally

This only happens when cold and the car idles with no issues when it is warm (maybe a slight hissing sound?). The car also seems to drive fine, and the mpg doesn't seem to be badly affected?

My thoughts are maybe a boost leak or a vaccuum leak? Potentially a seal might have become damaged that lets air escape when it's cold, but expands and seals the hole when it's warm?

I will try and get a video, but my engine is still warm from driving home

I would really appreciate any thoughts or suggestions. Thanks in advance!

Sent from my moto g( plus using Tapatalk

[Clarkj93]

Someone more technical will come along im sure but I would take a pure guess at the pcv valve and the pcv hoses, having started mine with it disconnected before by accident seems similar to yours where it was sputtering. Pcv's are common to go so if its don't been done ever or for a while and no other obvious ideas are thrown around may be worth changing for a new one and some pcv hoses as general maintenence and see of it fixes issue.

[owheel]

Nice one, cheers for the suggestion. I only got the car a few months back and I don't know loads of the history, so it seems like a good thing to do anyway!

Sent from my moto g( plus using Tapatalk

[LC5F]

Easy PCV test -
The crank case should be under vacuum, with engine running remove oil cap if your PCV is healthy there will be vacuum resistance for the cap to come out and the revs will stumble/die.
If you have a leak the oil cap is easy to take off and no change in idle.

[owheel]

Hi guys, I can't work out how to add a video via the app but you were all right. I replaced the pcv valve (super easy job) and the car is fine again.
Cheers everyone!

Sent from my moto g( plus using Tapatalk