Engine Pressure Popping Hose and MAS

My 2000 Blazer S-10 is having this problem. It started with the mass air filter sensor blowing out so I replaced it. Then, a month or so later, the car made a popping sound that was similar to when the MAS blew, but this time it was where a hose comes out of the top of the engine. The hose has a round cap that has OFF and ON marks where it should lock into place and leads to around the MAS. A secondary hose from it goes to the PCV valve.

I'm not sure what it originally looked like but I'm fairly sure it is broken because it will not lock on anymore. What happens now is, sometimes when the car is started, that cap will pop off and I must stick it back into place. If I don't, the car runs extremely rough. Exactly like with the bad mass air filter sensor.

I guess I could just get that cap part and replace it but it seams there must be a problem that caused the mass air filter sensor and now the hose cap to break.

Is there some excess blowby pressure from the engine on startup that could be causing it all? If that's the case I'm concerned that I'll replace the cap and then the MAS will blow again or worse.

I'd appreciate any ideas you guys can give. Thanks.

Welcome on your first post.
Sounds like you may have a problem but without seeing it I can not help much.
It might be a good idea to run it by a good repair shop and have them look at it.
May be a easy fix or major problem but it needs checked out.
Good luck and let us know how it goes.
MT

Can you post a picture of the cap that blew off? That might help us figure out what the problem is.

My 2000 Blazer did the same thing. It slowly became harder and harder to start and sometimes it would pop on start-up, blowing out the round plug you are describing that leads to the pcv valve. In my case, the problem was a bad regulator in the fuel injection spider assembly. It was leaking fuel into the intake manifold which would prematurely ignite and cause the popping. The new spider assembly completely solved the problem. It's not too difficult a job to do yourself (about a medium/medium-high skill level) and there is a superb how-to post here with lots of pictures which I printed out and used when doing the job. Of course, that is assuming you have the same problem. You first need to test your fuel pressure, especially the bleed down rate after you shut off the ignition. There are many posts here which describe how to do this test. Good luck and let us know what you find.

---Can you post a picture of the cap that blew off? That might help us figure out what the problem is.------

The plug he is talking about (I don't know the name either) locks into the top of upper intake manifold and if memory serves me correctly is about the size of an old silver dollar. It has two vaccuum hoses attached to it, one of which runs directly to the pcv valve. When it pops outs, it leaves the same size hole in the upper intake manifold, and amazingly, the car is still able to run although the idle lopes up and down wildly making horrendous sucking noises.

You just described it perfectly.

Is this the how-to post here?
(http://www.automotiveforums.com/vbulletin/showthread.php?t=559014&highlight=spider+assembly+regulator)

That is the post -- it is fantastic -- better than any book I've seen. The only problem I ran into was with that second step -- see where he has the 16mm wrench to disconnect the two fuel lines? There is no way I could get that wrench on the nuts because the firewall is too close. I quickly solved that problem by getting a dollar store 16mm wrench and cutting it in half with my angle grinder. Other than that, the job went off without a hitch. Also, make sure you carefully mark your ignition wires before you unplug them from the distributor cap because you sure don't want to mix them up on reassembly.