no vacuum hose should be collapsed at any time

also, I'm confused where you say "elbow on rear intake" and "I am assuming to be the non return check valve". On the Zetec engine, the PCV check-valve is on the front of the engine (facing the radiator), which then runs under the thermostat housing to the intake manifold.

 

My apologies for the confusion. You are correct about the hose going to the check valve. Recently bought the car and it was running rough so I did all the usual maintenance and tune up. I just learned that just replacing the PCV valve was not the end.

Was getting 28 mpg (147,000 miles) before tune up. 95% of the mileage is highway driven as I have a daily 90 mile commute.
After the tune up, I jumped to 31.5 mpg and thought all was well. Now I am only getting 29 mpg and I believe that this check valve is my issue. No CEL and car idles almost perfect with just an occasional mis.

 

that mileage is about right. Alot of folks report getting mid-to-high 20's for city driving and low 30's on the highway. I have an ATX and never do better than 34 mpg on a pure highway trip.

That PCV hose causes alot of problems for folks. If it's collapsed, then it might be the source of your occasional idle miss. It makes sense to replace it & the valve. The hose is absurdly expensive at the dealer (like fifteen bucks or so); if you're handy, you can jury-rig your own for a couple of dollars, or the last page of this thread discusses a third option:
http://www.focusfanatics.com/forum/showthread.php?p=4665595

 

FWIW - I've been told the factory replacement is updated with a heat shield wrapping now, might explain the cost a bit...

 

Here's the updated version. I think I paid about $20.00 at a dealership.

 

thanks for posting the pic!

 

That is hilarious, just last night I was looking at my pcv hose and needed that updated part number. Thanks Terry!

 

There is no check valve at that entry point, a simple tube entry. The check valve is the PCV valve itself, which is on the other end of the assembly up front. If tube truly messed up the idle should be affected first, as the small flow at that time is necessary to idle and keeping the IAC in its proper range. The tube very often will be collapsed but can run fine, it pretty much has to be 100% totally shut to have bad effect. Problem is, you can't tell the difference between one that is 85% shut and one that is 100%, simpler to just fix it outright. If almost all the way sucked shut you'll be there in a minute anyway. Often time the sucked shut part is soft like bubble gum and playing around with it will reveal a sucked-in hole that was leaking badly, but that can reseal to come and go and drive you flat crazy. I chased mine for 2 years before finding it, the problem came and went, when it was there it was bad, then mysteriously car would suddenly run perfectly again till next month when it would do it again. The collapse comes when the hose is bubble gumming up, it caves in from being weak and soft.

 

That is exactly how the hose feels. Would this have any affect on the inconsistent mpgs? I attempted to clean the EGR yesterday but was unable to due to the rusting. I am going to attempt to take the entire pipe off and clean it up that way. Thanks for the reply!

 

If idle not messing up it will not affect mpg, shows at idle far before other places. Cannot affect mpg and idle perfect. Now, if rough idle coming and going, yes possibly in that case.

 

Update - replacing hose today. I do believe my mpg issue was related to a dirty egr valve. After cleaning it up , mileage has improved dramatically. 160 miles on first quarter tank.

 

I'd agree that PCV would not have much impact on MPGs.
Now, with ZX3 you should quite easily average ~35mpg (or more, unless it's middle of winter), especially with long commute. Automatic will suck (as always, you can never low rev it the way you can with stick), with lead foot not even Prius get any good numbers.