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I have had for a long time an oil leak at the oil fill tube where there's a flange just on top of the left valve cover. Nothing to have oil dripping on the ground but enoug to mess up the valve cover and adjacent parts.

A few days ago I replaced the O ring there to stop the leak and here's what happened.

The idle speed rose slightly to normal and got a little smoother (it was slighty low compared to what it was when I got the car), about + 65 rpm. OIl pressure at idle was thus a little higher by a few psi.

Also it got rid of an annoying intermettent «miss» I had at idle one or two times a day: suddently the engine would act like it was firing on three cylinder's but only a few seccond at a tiime. This is gone.

All I can think of is that this leak at the fill tube created a small vacuum leak that slightly lowered the idle rpm, a condition that maybe got worse a few seconds at a time each time the PCV valve opened fully.

In case someone has similar symptoms, it's a 2$ fix.

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Glad to help but don't get too excited, maybe it wont work for you.

The description of what happened after I did the O ring replacement is fact. The explanation of why is just educated speculation on my part.

Hope it works also for you.

Nothing space age about this repair. You remove the two bolts hodiing the fill tube with a long extension (10mm head bolts and no nuts). You then pull on the fill tube (it's made of plastic by the way) and you'll see the O ring at the small end of it.

Replace, refasten, cross your fingers.

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I got similar results from sealing my dipstick tube with gasket sealer. Thought it was a freak, but mine is on an 83 brat.

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This makes sense because PCV hoses connect to the intake downstream of the flow meter, thus any air entering due to leaks would not be accounted for. But on the other hand, one would think a small leak like this one could be compensated for as a result of feedback from the oxygen sensor.

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