[mwillis]

I drove my car to work this morning and noticed that the idle speed seemed a little fast. Maybe a little rough, too, especially when in gear at a stop. I checked a lot of stuff, looking for vacuum leaks, or something holding the throttle open. No luck. A co-worker had me pull the PCV valve out of the valve cover while checking some of the same stuff. When I cover the PCV valve with my thumb, the idle comes down to where it sounds correct and smooths out. What could the problem be, if any, with the PCV?

[The Greek]

Replace the PCV with the correct on listed for your engine. PCVs are calibrated and installing the wrong one can create problems.
It's either the wrong one or it's gunked up and not seating properly, causing the vacuum leak.

[mwillis]

SO, I went out at lunch and bought a PCV valve. the result is the same. With the engine idling, and I pull the PCV valve out of the valve cover, should it be drawing a lot of air? When would it not do this? I assume since it is a valve then there are times that it should be closed, or that it should in some way meter the flow through it. I have a Holley 600, and the PCV is connected to the rear base of the carb using the original spacer. There are a couple of pictures on my profile where you can see the setup. I didn't have time to let it warm up to see what happens when it is up to temp.

[mwillis]

Well, last night I went home and played around with the PCV valve and hose. The factory hose is kinda short. Maybe it's an issue with a higher rise intake rather than stock height?? I cut the hose in an area behind the carb, before the 90 into the carb spacer. Then, I inserted a length of smaller diameter hose inside the larger one and replaced the 90 part. I added about 1" to the length of the hose. I also heated, bent and cooled the 90 that turns down to the valve cover, as this seemed to be a little too open of an angle. It now sets in the hole in the valve cover with a little less stress on it.
I have the cobra valve covers on it. The PCV grommet that came with them doesn't fit very well. A little loose. Does anyone else have this problem?
Lastly, I sprayed a little starting fluid around the rear passenger side base of the carb. There seems to be a little bit of a vacuum leak in that area. The secondaries are working, so I don't think it's the sec. diaphram. When I get back from the Mustang 45th, I'll take the carb off and check the throttle plate mounting. It's a fairly new carb, not one of the old gold colored Holleys.
Right now it's doing pretty good. Idle speed is normal, and smooth idle at a stop, in gear.
Mike

[madmonkey]

Hate to dig up an old thread but I am having similar issues.

I had the carb cleaned and tuned and when I got it back it worked great and idled smooth. After a while the idle slowly started to get worse and I started to poke around under the hood.

I noticed the grommet for the PCV value was so old it was brittle and hard no longer rubbery and the valve slid right out. So i ordered a new hose, new grommet and order a PCV valve from CJ Poneyparts.

Anyway the idle is worse now, no matter how I adjust the idle mixture screws it is still not smooth, but when I remove the PCV valve and plug it with my thumb it smooths out perfectly.

What could be the problem here?