> I have a 1991 Ford LTD Crown Victoria with a 5.0 V8 that will not idle.
> It will only run if I press on the accelerator right after it starts to
> keep it at a higher RPM. Seems to run fine at a higher RPM. When I let
> up on the accelerator, it goes to a very slow idle and runs rough, like
> it's missing, and then it stalls. There's no "check engine" warning
> light. I'd like to get it to idle temporarily so I can move it to a
> loaction where I can work on it. Will turning the throttle plate
> adjusting screw raise the idle a bit? What might be the source of the
> problem - spark plugs, bypass air value, EGR valve??? Thanks!
The IAC valve (or Bypass Air Valve) is most suspect on Fords with poor
idle quality. If you had to shotgun one part, that would be it. Don't
randomly mess with the throttle blade stop screw. There is a procedure
for setting it, but if it hasn't been touched, then just leave it alone
Also check your TPS voltage reading. It's best to check it at the ECM,
so you will need a wiring diagram. Look for .35 to .5 volts at 0%
throttle. If there are any devices that open the throttle when the
engine isn't running, you will need to be aware of them. Ideally, you
would check TPS voltage *with* the engine running to compensate for
engine vacuum on the throttle blade, dashpots, etc - but in your case
that isn't possible.
Look/listen for gross vacuum leaks as well. Check around major
sources, like the PCV hose, broken PCV valve, intake gaskets, brake
booster and hose, etc.
Toyota MDT in MO