[T3] '72 FI won't idle down

[David]

Today I had several nice long conversations with Gemini, and I learned a few things that clarified to me what the 3mm restriction is that talked about in these reply’s. I know Gemini isn’t always correct, so correct me if needed.

Gemini said that only the ’72 & ’73 ( newly added PCV system to existing engines ) IAD front cover plates have now been repurposed with a very small restriction designed into them that regulates the flow of air being sucked into the IAD through the ’72 & ’73 only PCV valve. This same front cover was used in pre-‘72 models for a different purpose (non PCV engines), but in order to use this front cover this time to regulate air flow from the PCV - they needed to neck down the flow of air being pulled through the wide open PCV valve. This is where MY ’72 system has a problem because my engine actually has a pre-’72 cover plate with the .312” “orifice”: so it is trying to suck way too much air through the PCV valve! No wonder I have never been able to get this engine to idle down correctly.

And here I thought I had every correct ’72 component on my ’72 engine. It turns out the ’72 & 73’ IAD has the same part number on the casting, but VW changed the front cover plates starting in ’72, even there is no part number stated on the cover plates….. They simply used the correct cover plate for the PCV equipped cars. In my case – someone changed the IAD cover plate & I did not know the difference.

So this is where this 3mm orifice restriction applies. I’m going to figure out the best approach to getting this restriction into my engine….. probably along the lines of what Keith did. I do not want to destroy my PCV valve because they are unobtanium, so I’ll add the restriction elsewhere.

Interesting thing is Gemini said (several times) that the restriction orifice was 4.5mm in diameter, so if there is anyone out there that has a ’72 or ’73 end cover plate in their possession that can measure this orifice: that would be awesome information to have. The catch here is the cover plate would need to off the engine and separate from the IAD in order to measure this little orifice….. But I thought I’d ask 😉

Dave Pallo

’72 Square ~ Elwood

Fairport, New York

 

 

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