I re-fitted a K&N stub stack I used to use.  After changing to a different filter assembly, in order to fit taller spacers a couple years ago, it didn't fit with the new air cleaner base, so I have been running without it.  I took a closer look and figured out what I needed  to do to make it fit.  I don't see how that could cause this, but it's all that I changed before hand.

During one  part of the the test drive to evaluate things, I accelerated hard onto an interstate style highway, it has on and off ramps, held it at about 3000rpm for a half mile, to the next exit.  When I got to the exit, it would not idle below about 2100-2200rpm.  I did what I could in the moment to see if the pedal was stuck and it did not seem to be.  It ran fine on the way home.  It just would not idle below that rpm.  When home, I turned it off to gather tools to investigate and, of course, when I start it up, everything is back to normal.  I've been on a couple test drives, trying to duplicate things, and everything remains fine

It's about a 1400rpm increase over the normal idle speed so the only explanation I can come up with is that the throttle was held open some how.
If it were a vacuum leak that large, it would run terribly but it seemed fine, other than the high idle.  I also don't know of vacuum leaks that  just fix themselves.  I've checked all the gaskets  and vacuum hoses and caps the best I can for evidence of some very odd failure but don't notice it.
Timing can affect rpm, but I don't think it can affect it that much, and again, it doesn't usually fix itself.  I checked timing and all looks normal.
The primaries are operated mechanically, but the secondaries are vacuum.  I do not feel any bind if I operate the primaries or secondaries, pedal linkage attached, by hand and there is nothing that I can see that might cause it.  If I'm not mistaken, if the secondaries stick partially open, it can hold the primaries partially open, which might result in a situation in which vacuum is being applied to the secondary diaphragm, and may not release until the engine is shut off, eliminating the vacuum source.  Is that plausible?

At this very moment, it's running great, possibly better than ever.


Lawrenceville, GA