XJ6 Series III - bad idle / false air

["A. Gardner" <gardnera@SLU.EDU>]

On reading the rough idle posts I was intending to restate my post of a few
weeks ago regarding "false air" as a possible cause but OOPS, upon
rereading, I find I owe the list in general, and Eric Deci in particular, an
apology for an omission. 

I wrote (in regard to an XJ6 Series III but it would probably be applicable
to other FI models):

If the injector grommets / seals are bad you will get "false air" i.e. air
that is not measured by the air flow meter.  Consequently, the ECU will
signal too lean a mixture for the amount of air entering the manifold and
this will certainly contribute to poor idle.  The easiest method I have
found for checking false air is as follows.  Attach a piece of tubing to the
intake manifold, I use the connection for the thermal valve (orange thingie
on the fuel rail).  Then, with the engine stopped and dead silence in your
garage (seriously), blow into the tube, crimp the end, and listen.  You will
hear some of the residual pressure exit through any leaks and can confirm
the location with soap solution.  (I did not find it necessary to block the
tailpipes).  I assure you, it only takes a pound or two of puff to play
music with your air leaks.

What I omitted, is that before blowing, I remove the air filter and seal the
inlet side of the air flow meter using a three inch diameter rubber end cap
as used for standard PVC drain pipe.  These are sold in all hardware stores
here in the U.S. and are usually supplied with a hose clip.  They seem a
little large for the inlet the of the air flow meter but the clip will
squeeze the soft rubber down until it is airtight.

If you have been blowing into your intake manifold without capping the AFM,
mine will not be the only face that is red.  Again, my apologies to Eric and
the list.


Tony Gardner
XJ6 Series III (1986)

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