> Here's the problem. (10 pts) Suppose there IS an air leak
> between the plenum chamber/intake manifold (I have good reason to
> suspect that area). Will that make the idle speed go UP or DOWN,
> everything else being equal? Why?
The mixture is controlled by the air flow meter. A stoichiometric
mixture of air and fuel must be maintained, and the amount of air
going into the engine is the biggest component of that mixture. Your
leak would cause the computer to think that there is less air flowing
than there actually is, making the engine run very lean. This would
tend to reduce idle speed.
If you stick your hand into the airbox and press that little flap inward
a bit (I'm assuming that your airbox is similar to Jaguars') you should
notice your idle increase and (more importantly) smooth out, if an air
leak is your problem.
>
> The car currently lacks low end power and has kind of a flat spot
> (it drives just like an Alfa) so I'm inclined to say that I have
> an air leak NOW.
The more obvious symptom of a bad air leak would be driveability problems,
which you do indeed seem to be suffering from.
Before taking anything apart, I would figure out where the leak is. Spray
with carb cleaner, feel around the back of every joint to make sure a
piece of gasket didn't fall while you were bolting something on, etc.
There is no reason that you shouldn't be able to figure out where your
leak is within an hour at the most, and you might save yourself a bunch
of wrenching.
Joe
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