To find the intake air source just remove the intake hoses from the TB (both 
main and idle air).  Cap off or plug the TB's idle air inlet first.  If that 
makes the engine stall then then the IAC is bad or isn't being driven by the 
ECU*.  If the engine doesn't stall at that point, cap off the main TB air inlet 
using a suitable-size jar lid with a soft rubber seal (either molded-in seal or 
a separate gasket.  If the engine stalls at that point the air is leaking 
around the butterfly.  If it doesn't, you'll be able to hear where the air is 
leaking into the manifold.
* There were two IAC suppliers and one of them provided a unit that defaults to 
high idle if the electrical drive system fails.  The other provided a unit that 
defaults to the engine-stall position.
  ----- Original Message ----- 
  From: [email protected] 
  To: Ben Gleason 
  Cc: [email protected] ; [email protected] 
  Sent: Thursday, May 06, 2010 6:29 AM
  Subject: Re: 94 turbo Miata with high erratic idle


  Guys, couple of other datapoints:

  Unplugging IAC it holds steady around 1500-1800
  Plenty of vacuum to MAP box
  Keypad reads MAP correctly, something like 30ish at high idle, builds 
15-17psi at WOT
  Idle adjustment screw doesn't do much of anything, it's about 1 turn from 
fully closed
  Idle switch is perfectly set, flips * at slight throttle touch
  I believe keypad reads 45% on idle screen (not sure that I remeember right 
but I think that was it).
  ECU chip is not newest, maybe 2 years from newest one I believe but when I 
looked it up the revisions really didn't seem to matter

  Wallyman




  Ben Gleason <[email protected]>


                Ben Gleason <[email protected]> 
                Sent by: [email protected] 
                05/06/2010 09:19 AM

       

              To 
              "[email protected]" <[email protected]> 


              cc 
             


              Subject 
              94 turbo Miata with high erratic idle 
              
       

  I have a 94 turbo Miata with the Link ECU that has always had a high idle 
since I purchased it late last summer, but recently that high idle is now 
erratic and it bounces from 1900 to 2100 rpm (fuel cut off I believe) My 
friends and I cannot find a vacuum leak, and believe the IAC is working 
properly. 

  Does anyone have any ideas how I can fix this annoying and embarrassing 
problem?

  Thank you,

  Ben
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