Idle change when removing oil cap

[svocudd]

I recently noticed idle speed change when removing my oil fill cap. THe RPM levels drop slightly. I replaced the original PCV valve last year with the correct Motorcraft item The car runs fine. Anyone experience anything similar?


Cudd

[SVOeric]

depending on how much you run your car, a yearly change of the PCV may not be enough.

Crankcase pressure is the only reason I can think of for the idle to change.



I could be wrong tho

[russde]

Sounds like a vacuum leak

Mine does this too, found out last week.
It makes the car sound like it has a vacuum leak, not a horrible one but enough to make the idle kind of screwy.
On a side note, my car will usually idle rough for ten to fifteen seconds when cold, sometimes almost dying. Those mornings on which I have to add oil before starting the car the idle is perfect. Related? Your guess is as good as mine (if it's better I'd love to hear it .
Russ
'86 9L

[SvoTy]

Re: Idle change when removing oil cap

Originally posted by svocudd
I recently noticed idle speed change when removing my oil fill cap. THe RPM levels drop slightly. I replaced the original PCV valve last year with the correct Motorcraft item The car runs fine. Anyone experience anything similar?


Cudd

Mike it is the same thing as a vacuum leak. The umetered air going into the engine without going through the vane meter makes it stumble. The same thing happens when you install one of the "breather kits" on the back of the valve cover.

The computer will eventually learn the leak and try to smooth it out but the processing tables that it picks out its strategy from will be out of whack.

We need to get Ryan Cloud to do a story on this in the FAQ section. He explains it very well.

[ZENSVO]

I recently found a similar problem with my'86. I was trying to remove the oil cap with the engine running and found a lot vacum sucking the oil cap to the valve cover, like a vacum cleaner. Finally checked the pcv valve/hose and found the bottom of pcv valve was gone, no check valve or anything, just a straight shot thru the two hoses. Put a knew pcv valve in and the vacum at the oil cap is alot less. Also, should there be vacum at the oil filler cap?
thanks