I think one or both of the previous mechanics have already messed
with the AFM -- the black plastic cap can be removed with gentle
pressure, and the adjuster screw plug has already been drilled out.
Maybe it's just a crudy rebuild and can't be adjusted back into spec?

Also, I notice that at idle, the spring bounces all over the place,
but the idle seems to smooth out a bit if I hold it steady.  Is that
normal for it to vibrate like that?

Thinking maybe I should just buy another AFM and do the debug-by-
parts-swap method...?

On Aug 10, 2006, at 4:07 PM, Kenneth Lewis wrote:

> Michael,
>   Just because the AFM is rebuilt doesn't mean it's good. Possibly the
> spring is not tensioned correctly. I wish there was a good
> procedure out
> there to tune them. Here are some things I have learned by
> experimentation.
> YMMV.
>
>   First you need a good voltmeter and O2 sensor. The three throttle
> body
> alignments outlined in the Bentley should be checked. Carefully pry
> the
> black cap off . If you don't mess it up too bad it will go back on
> and stay
> without glue. Drill out the plug so the allen screw is accessible.
> Use an
> allen wrench and determine the base setting of the allen screw.
> That is,
> find out how many turns until it bottoms out so you can return to
> where you
> started, just in case. Write it down. Likewise mark the black
> plastic wheel
> so you can return it to it's original starting place.
>   The engine has to be up to operating temperature. Disconnect the O2
> sensor and hook up the voltmeter to it. If it is running lean the
> reading
> should be near zero. Ideally the voltage should toggle equally
> between zero
> and (about) one volt.
>   Off the top of my head I can not remember which way to turn the
> wheel to
> enrich the mixture. I noticed that after a few notches in the right
> direction the engine RPMs picked up and smoothed out. Unfortunately
> the
> spring tension that equated to the best sounding idle did not give
> the best
> reading from the O2 sensor. This is the part where I wish I had a good
> procedure written out. I fiddled with the spring tension and idle
> screw (on
> the throttle body) until I got a happy balance between idle and
> good O2
> sensor output. Use the allen screw to fine tune the O2 output voltage.
> Hopefully the output is good at higher RPMs, otherwise you need to
> adjust
> for that.
>   I run through this procedure every year before vehicle emissions
> testing.
> Good Luck,
> Ken Lewis
> http://neksiwel.20m.com/ (more O2 info here)