Rough Idle & P0171 + P0174. Vacuum leak?

[Anker]

If you couldn't get the oil cap off while the engine was running you have a failing AOS. Get it replaced before you destroy the engine.

[geraintthomas]

Originally Posted by Anker

If you couldn't get the oil cap off while the engine was running you have a failing AOS. Get it replaced before you destroy the engine.

And would a failing AOS let in air, giving the lean CEL's? Could this be the problem for everything?

[911monty]

Originally Posted by geraintthomas

And would a failing AOS let in air, giving the lean CEL's? Could this be the problem for everything?

The oil fill pipe can collapse/ crack from the excessive vacuum in the crankcase when the AOS fails as yours appears to have done.

[geraintthomas]

Originally Posted by 911monty

The oil fill pipe can collapse/ crack from the excessive vacuum in the crankcase when the AOS fails as yours appears to have done.

Surely if the oil filler pipe is cracked, then the engine wouldn't sound much different if I ran it with it removed? It stalls when I remove it, showing there's a huge difference when it's in place.

Would a faulty AOS cause a vacuum leak?

[Anker]

Originally Posted by geraintthomas

Would a faulty AOS cause a vacuum leak?

Yes! The reason why you can't get the oil cap off is because the inlet is sucking air out of the crank case through the split AOS diaphragm.

[911monty]

Originally Posted by geraintthomas

Surely if the oil filler pipe is cracked, then the engine wouldn't sound much different if I ran it with it removed? It stalls when I remove it, showing there's a huge difference when it's in place.

Would a faulty AOS cause a vacuum leak?

I'll let the master answer those questions in the attached thread. The squeak or hiss you attached in your first post could be from your front main seal.

Did I toast the engine?