Massive suction through oil fill

[stageone]

I have a 2000 LeSabre with the 3800, recently it started to make a noise intermittenly that I though was without question the belt slipping. That high pitched squeel we have all heard. The belt is new (less than 2k on it) so I thought the tentioner or an accessory was maybe going bad. As I was trying to figure out which, I realized that the nosie was not comimg from the belt at all. I'm not sure where exactly it is coming from but I could tell that it was on the driver side of the engine maybe near the throtle body and I went to take the plastic cover off the top of the engine to see where. As I opened the oil fill cap so I could remove the cover I found the cap to be under a huge amount of suction and difficult to pull off, but when I did the sound went away and after a brief stumble, the car ideled perfect. I set the cap back on and the idel goes up and the noise comes back. I also have been using a bit of oil and wonder if this suction is maybe pulling oil up and out somehow as there are only 85,000 miles on the cas and we got it new and never has used a drop before and there are no leaks. I got the codes from the check engine light and there are 2 each of PO138 and PO507. Thanks for reading hope someone has seen this before.

[maxwedge]

Check the pcv and seals under the map sensor on the intake manifold.

[Tech II]

I agree with Max.......The Map sensor housing untwists counterclockwise.....pull it up.....should be a large orange colored o-ring there....then remove the PCV valve....there should be a small black o-ring around it(may be stuck in the hole)....check PCV valve that it is ok and that both o-rings are in place...

Recent tuneup or work done on upper plenum?

[HotZ28]

Click Here for more info.

[stageone]

If fact yes, I relpaced the upper intake due to warpage where it connects to throtle plate I guess its called and coolent leak. A new map came with the plenum I believe but I don't honestly know if I got a new PCV. I have put a couple thousand miles on it before this problem started. I took a look at the link posted by HoyZ28 (very helpfull) and I will pull it apart and check the valve out asap and let ya know how that goes. Thanks for the help at least I have some directon to head in now. If I have to drive it should I leave the dipstick pulled out a bit or something, I dont think it would be great to do but not as bad as leaving the oil cap off and risking crap getting sucked into the motor.

[stageone]

OK, thanks to all for the help. The car is fixed and running great and it only cost me $3.17 tax included. The only bad part about it is the fact that it was all my fault. As I said, the upper intake was replaced not long ago and a new map sensor did come with it. On my way to the shop I picked up a new PCV valve as I said to my self, if I'm going to pull the old one out I may as well just throw a new on in there for 3 bucks. So as much as I hate to say it, when I pulled the map housing off the car I was shocked to see that there was no PCV in the car! I blew it in the first place! It took me longer to find my o-ring kit (the new valve did not include one) then it did to do the whole job and it is of course running perfect. I cleared the codes and that was that. Funny thing is as I was putting the o-ring kit back where it should have been in the first place what did I find? You know it, the PCV valve that was included with the new upper still in its sealed plastic bag. Stapled it to the wall above the work bench as a reminder to double check everything every time. I hate to think off all the fuel I wasted and the oil use is explained as well. Lesson learned, I'm so ashamed!