Re: [DML] Missing idle mixture screw?
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Re: [DML] Missing idle mixture screw?

vin4258 wrote:

>Vin 4258 failed emissions a few weeks ago and after doing a tune up
>(plugs, wires, cap, rotor, air filter, oil) it failed again today with
>only minimil improvement.  Emissions tester says he thinks the O2
>sensor is ok because emission levels pass at high RPM (the
>sensor 'kicks in' at a higher RPM but does not affect idle mixture?)
>Next option is to adust the idle mixture screw, but when I go looking
>for it, it seems to be missing.  All I see is a hole with no apparent
>end but I do see threads.  What is this and can I simply put in a
>replacement screw or does this need major work?  I have never messed
>with it and the car only has 7k miles on it and this is the first
>emissions testing I have been required to get since I bought it...
First of all, need to make sure your actually talking about the idle
mixture screws.  These are them here:

and as John Hervey's image states, they should be snugged down and
shouldn't be adjusted. If you are missing one, then that is likly your
However. I get the feeling your really talking about the mixture
adjustment, shown here"

if so. Then the adjustment screw is pretty deep down, and you'll require
a dwell meter at the minimum to adjust it properly.

Just remember that the acess hole you insert the allen wrench to adjust
this should be plugged at all times. If it's open its just another air
leak that throws off the mixture. You also want to be positive you don't
have any other vacuum leaks as well.  Another thing to consider is if
your mixture was really rich for a long time, you might need a new
catalytic converter.. They don't fare too well when the mixture is much
out of the proper range.


VIN# 03209

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