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--></style></head><body lang=EN-US link="#0563C1" vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt'>Thanx for all the help so far, guys.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Correct me if I’m wrong, but based on what I think I know; I have ruled out any air leaks AHEAD of the PCV valve (where crankcase vapors are entering the PVC valve). The PCV valve is THE regulator of how much crankcase air that gets sucked into the IAD. The PCV valve has a fixed diameter orifice, and what air gets through it - all goes through to the IAD. It must be a fixed flow rate, as anything other than a fixed rate would result in throttle wavering. The PCV valve does not care where it gets its inlet air from – it is only going to allow so much air to pass, and what gets through the PCV valve is it. There can’t be any leaks AFTER the PCV valve (on the vacuum side of the PCV) to the IAD, like through the rubber hose & metal pipe coming out of the front of the IAD, because then you would be introducing an unregulated amount of air. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>To demonstrate - I can totally remove both air hoses off the ’72 heads and it will have zero effect on idle speed, as the PCV is still letting the same amount of air pass through it. Any air leaks on or around the crankcase won’t matter for idle speed, as the PCV is still getting all the crankcase air it will allow to pass through. I could remove both valve covers entirely and it won’t affect idle speed. Correct me if I’m wrong, but there isn’t even a seal on the back end of the crankcase. Of course you want the PCV system to work on these cars, so yes it is important to have tight hoses and gaskets and seals in order to have a proper functioning PCV system, but air leaks to the crankcase should not affect idle speed. Please correct me if I’m wrong about this.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>I have followed Jims advice through the years, and I do have all the correct intake phenolic plates & seals installed. I did align all the intake runners, and I put the runners rubber hoses on with a rubberized gasket sealer. I can spray carb cleaner everywhere all around the IAD, runners, hoses, injectors….. anything to do with the intake system, and no change in idle RPM.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>My throttle plate is closing fully, because if it did not fully close – the orifice at the very bottom of the IAD opening which supplies idle vacuum to the retard side of the ’72 distributor would not see any vacuum. The throttle plate MUST be fully closed in order to get a vacuum source at that one port.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>So today I tried my backup brain, and it made zero difference in idle speed. Just as Jim says: he’s never seen one fail. They either work or don’t – nothing in between </span><span style='font-size:11.0pt;font-family:"Segoe UI Emoji",sans-serif'>😉</span><span style='font-size:11.0pt'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Next I measured the resistance of both temp. sensors, but only in the “hot” state. Intake sensor was @ 139 ohms hot, head sensor @ 540 ohms hot. A little off of spec., but I’m thinking not enough to cause this idle issue. I’ll check the “cold” resistance tomorrow morning.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Now I looked at the idle speed screw & its “passageway” in the IAD. The working end of the screw (restricting air into the IAD at idle) is a .272” diameter shaft (with a rounded head end) and this fits into what I measured (with drill bits as pin gauges) a ~slightly loose~ .281” opening in the IAD. I own a few extra IAD’s, and they all measured the same on the screws and the openings. I took an extra idle screw and used a drill press to sand down the shaft to a .265 diameter, so that when I installed heat shrink wrap over this end: the end is now .284 diameter. Installed this into the IAD and now my idle is down to about 980 rpm, as this now larger diameter idle screw end took up the .009” interference that I saw in my measurements…… I’ll take it!<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>So now I’m going to use my buddy’s lathe and turn down a 10mm x 1.5 screw to this bullet end of .284” diameter and see if I get the same idle results.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>It still bugs me that I did not come up with a positive assignable cause for the high idle, but I’m good for now </span><span style='font-size:11.0pt;font-family:"Segoe UI Emoji",sans-serif'>😉</span><span style='font-size:11.0pt'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;mso-ligatures:none'>Dave Pallo<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;mso-ligatures:none'>’72 Square ~ Elwood<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;mso-ligatures:none'>Fairport, New York<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p></div></body></html>