Miata Mailing List: February 1994, Message #91
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   From: tkacik@adtaz.sps.mot.com (Thomas Tkacik)
Subject: Re: Engine Bogging on Slowdown
   Date: Mon, 7 Feb 1994 09:51:35 -0500


>A common ailment seems to be near stalling upon deceleration.  It comes
>up regularly here and in Miata Magazine.  Earlier this week someone
>posted a message listing dealer fixes that temporarily solved the
>problem.  The word "temporary" reminded me of my own diagnosis.

>Notice that the ISC (in particular its air-bypass openings) is
>positioned at the bottom of the throttle body - where it can naturally
>catch passing crud in its mechanism.  Now notice that the breather hose
>from the driver's-side (U.S. spec) of the cam cover feeds blow-by
>gasses to a point right over the throttle body & ISC valve.  The
>blow-by gasses can be slimy.  Run a Q-Tip around the inside of the
>breater hose to see what I mean.  I think that some of this crud gets
>into the ISC valve, and interferes with its smooth operation.  It
>probably doesn't take much crud to have an effect.  Changing the ISC
>will fix the problem, but only temporarily - until sufficient crud
>again accumulates.

Perhaps the solution is to add cleaning the ISC at each oil change.
Make it a standard part of a tune up.
I think I will check this out on my Miata.  I have been having this
problem occasionally, (though not enough to make me do anything
about it).

Tom Tkacik
tkacik@adtaz.sps.mot.com