Engine Today I found air leaks on 2 different IAC's which caused erratic idle issues.


Active Member
Dec 17, 2021
Hello all . For a lil bit I was trying to track down a pesky airleak I knew I was hearing but even with a stethoscope couldnt seem to find it..

Today I got scientifically midevil on my approach and it paid off...

I took one of my IAC's and bolted it to plexiglass drillled a hole on one side and added a hose barb then tapped and JB welded it in to be leak-free then slapped on my handheld vacuum pump and pulled it to -10 inches and it quickly dropped to Zero so I took it apart and this is what I found...

Right here in this area on this Duralast brand IAC there is an o-ring to seal this area but the o-ring that was installed wasnt thick enough to properly seal against -10 inches of mercury so I used a thicker o-ring from a fuel injector seal and retested..


This time the vacuum held alot better and dropped to zero slower than the first time so I put the body in water and added pressure and low n behold I found 2 more very tiny airleaks and they are the tiny dimples where the end cap is only crimped on.....I sealed the endcap with clear all-purpose epoxy and then retested and it held vacuum...


Then the other issue was the weak power of the pusher spring that held the plunger against the IAC body to create a seal when closed but it had quite a bit of air getting by the plunger so I calculated in my head about how much air was getting by the plunger seal and I made a new gasket with smaller holes using a paper hole puncher to control the rate of air so the IAC can control idle faster and more accurately..


All of the fixes/changes paid off as now my idle is very steady with my abnormal idle symptoms gone.....

And just to further this scientific study I took another IAC a Ford Motorcraft one that was giving me similar idle issues and found something very interesting too.....Under this black looking cap is a tube thats completely open and the cap allows some air to get past so I put JB Weld in the lil hole on that IAC plus snapped the black cap back on and when tested both of them now work as intended and gave no issues like they did prior................

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Very interesting! Thanks for sharing. My 87 still has some idle issues I have to do more diagnostics on at some point, but I had an accident last week and cannot use my right hand much for the time being. It was the usual cold start/ stall issue, but last time I ran the car it had a very slight surge issue.