'73 PCV valve leak, High idle even after throttle body rebuild Options

[chmillman]

Hi all,

So still working on the FI, have gotten a lot of stuff fixed. But, despite rebuilding the throttle body to fix an air leak around the worn shaft, the idle is still too high even with the screw turned all the way in. My FI guy did some research and found that the PCV valve is leaking. He put a constrictor clamp on the hose from the PCV valve to the intake manifold and adjusting that brought the idle down.

Apparently the configuration on the '73-'74 motors was to route the output hose of the PCV valve directly to the intiake manifold, whereas before/after the hose just went to the air cleaner. So if there is a leak in the system, it can cause idle problems - I guess that's why they changed it...?

Anyway I found this 5 year old thread here:

http://www.914world.com/bbs2/index.php?sho...c=347986&hl

Again apparently, since the original PCV valve is NLA, there was a suggestion that it be replaced with a Toyota part - haven't checked if it is still available. Is that still the current thinking? Having read the thread, I am a bit worried about the potential overpressure/underpressure problems it could cause...

Other possibility I guess would be to eliminate the PCV valve entirely and pipe the hose from the oil filler neck directly back to the air cleaner, and plug original hose entry into the intake manifold ?

Any other suggestions? TIA!

[emerygt350]

The active pcv (what?) is actually pretty clever. It should be causing a slight increase in your idle. That is the way it was designed. Even at idle it is drawing gasses off of your crank and heads. That is part of the problem with after market, that idle bleed needs to be a specific volume. Anyone with an active pcv will notice an idle drop if you plug it. It is a dead simple device. Pull it, clean it, put it back in. If you plug it and your idle drops from (what? Have you told us what your idle is now?) to 750 or so, you know it is all the pcv. If you plug it and your idle drops to 900-950 something else is causing the high idle.

Even with a perfect motor, a rich mix and/or timing, particularly timing, is going to cause a high idle. Remind me, 123ignition or stock? Are you certain your retard/advance is setup correctly if it's stock? Are your weights sticking?

Put a timing light on it and see what kind of advance it has at idle (with everything connected).

[Lockwodo]

I installed a FRAM FV279 PCV valve in my '74 2.0 a few years back, no kicks or complaints.

[emerygt350]

I installed a FRAM FV279 PCV valve in my '74 2.0 a few years back, no kicks or complaints.

was that plug and play or did you have to mess with it?

[Ishley]

I did the Toyota PCV valve and it works well. I ordered several so I have backups. like $5 here in the US.

[Lockwodo]

I installed a FRAM FV279 PCV valve in my '74 2.0 a few years back, no kicks or complaints.

was that plug and play or did you have to mess with it?

Direct fit. I replaced the PCV valve and the grommet at the same time.

[emerygt350]

I installed a FRAM FV279 PCV valve in my '74 2.0 a few years back, no kicks or complaints.

was that plug and play or did you have to mess with it?

Direct fit. I replaced the PCV valve and the grommet at the same time.

Where did the grommet come from?

[Ishley]

Amazon for the grommet.

[emerygt350]

No modifications needed?

[Lockwodo]

A direct replacement, no mods needed.

[emerygt350]

Interesting! I might give it a go and see what happens...

[JamesM]

IF you go the route of open venting the crank case to the air filter there are a few other things you should do as well.

First PLUG THE HEAD VENTS!

Second, get the later style (75) larger oil tower vent.

The number of cars I have seen with improper crank case venting setups at this point is mind boggling. The vented heads sort of work alright when there is vacuum on the crankcase but take away the vacuum and don't increase the vent size, the crankcase starts venting pressure (and liquid oil) out the head ports. At sustained high rpm this is bad enough to vacate the sump and starve your oil pickup!

[chmillman]

We've decided to go with the Toyota substitute PCV valve approach. Took some searching to find an equivalent here, finally did - at 10x the US price (IMG:style_emoticons/default/sad.gif) - but available immediately. Will know more on how it goes next week.

[emerygt350]

We've decided to go with the Toyota substitute PCV valve approach. Took some searching to find an equivalent here, finally did - at 10x the US price (IMG:style_emoticons/default/sad.gif) - but available immediately. Will know more on how it goes next week.

I would try the cheap fram and grommet personally. I have tried the toyota and it required mods to the grommet and it didn't work very well. So badly I just cleaned up my old one instead.

[emerygt350]

and did you make sure it is actually the pcv?

[chmillman]

Well, we tried to find a Fram 279 equivalent. This is what’s coming…

Definitely a Toyota part according to the images. No idea if it will fit, the car is not here.





And yes, the PCV valve is at least part of the problem as far as we can tell.

[Ishley]

This is what I have and it works good for me. I actually replaced the Fram one I originally installed with the Toyota because I thought the Toyota worked better.

[emerygt350]

I know I had a conversation with one of the old hats on this but but I am sure it is buried among those threads. This is not an equivalent. The original had specific levels of flow base on vacuum etc and you can only hope the spring in this matches those. A Toyota is going to have a much softer job pulling vapors than an air cooled 50 year old engine design. So buyer beware. I really don't think it will matter, but just a heads up.

Again, you say it is the problem but the pcv is a intentional leak on these motors. Before I dumped 30 dollars to get a pcv I would just plug it and see where I am at. If your engine is not doing something it shouldn't be it should drop to around 750ish without the controlled leak of the pcv. If it isn't doing that then this is a waste of money.


What is your high idle?

[Ishley]

I don’t disagree. I would love a good stock one. Everything I found when I searched was a knackered up used one at some crazy price point… (no guarantees and no returns). So we’re left to McGyver a solution. When I pull the hose off my “Toyota” solution… I get no change in idle. So it’s as close as I can reasonably get in the world we live in. Do anyone have a better solution?