no oil cap still run ok?

this is for a buddy of mine but last weekend he was changing his oil and he went to start it and it wouldnt start, so he stoped and went back under the hood and saw that he had forgoten to put the oil cap back on so he did that looked at a few other things and then tried to start it agian and it started right up so ya he let it idel for a few min and then shut it off and went and took the cap back off and tryed to start it agian and it wouldnt start. put cap back on, started, left running took cap off car ran like shit and when i say it ran, it barly ran, put cap back on and ran fine.
is this normal ? wut could cause this?

this is the weirdest thing i have ever heard, i thought he was lieing but he showed me and ya he wasnt lieing it did it when he showed me

92se 180,000mi

Because of the emission control systems on cars the oil cap is very important. The PCV works on vacuum and when the oil cap is off the valve does not work properly and allows air to enter the engine at a higher than designated rate. The same occurs when the egr valve works. It appears that the car is extremely sensative to low vacuum and therefore when the PCM senses the presence of air in greater than designed quantities it will not allow the car to start.

My car doesn't have an oil cap.......it has a 710 cap. :lol2:

this is for a buddy of mine but last weekend he was changing his oil and he went to start it and it wouldnt start, so he stoped and went back under the hood and saw that he had forgoten to put the oil cap back on so he did that looked at a few other things and then tried to start it agian and it started right up so ya he let it idel for a few min and then shut it off and went and took the cap back off and tryed to start it agian and it wouldnt start. put cap back on, started, left running took cap off car ran like shit and when i say it ran, it barly ran, put cap back on and ran fine.
is this normal ? wut could cause this?

this is the weirdest thing i have ever heard, i thought he was lieing but he showed me and ya he wasnt lieing it did it when he showed me

92se 180,000mi

i forgot my gas cap once, I think i got 9mpg all the way to school. But my car cranked fine, the idle just went down to like 550

So then what happens when you see some of the guys with breather caps in place of the oil cap? How does that work? And whats the point of it?