Contour Enthusiasts Group Archives Forums General Troubleshooting Idle Speed

My daughterâ??s Mercury Mystique 1995 with 2.0 engine registered 500rpm at idle where
it should have been at 900. In park and neutral, it still idles at 900 but drops to 500 in
drive. An acquaintance of hers, a â??shadetree mechanicâ??, where she attends school (100
miles from here) did her a favor and adjusted the accelerator to increase idle speed. It
now idles at 1000 without load and 600 in drive. This would be a masterful stroke of
blind luck if the computer respected what the fella was attempting to do. Unfortunately,
normal cruise speed has been disturbed since the owners manual warns idle speed is
under computer control and no manual adjustments are permitted. I would like to restore
the accelerator to its original factory specs - any idea how to do this?
Ps. The original problem was caused by a faulty oxygen sensor straight from the factory.
It never caused CEL or registered a trouble code. It was a [censored] to track down.

My suggestion on how to restore the throttle stop to its original condition is to start the engine and allow it to come up to temperature (until the temperature guage stops rising) and back off the idle stop screw until the original no load idle speed is obtained.

The throttle plate should be fully closed, the IAC controlls idle speed.

A tang on the throttle shaft will hit the the throttle body casting when it is closed. Usually there is a throttle stop screw to adjust. On units without a throttle stop screw, bend the tang to allow the plate to close.

You must remove the intake hose so you can see the plate.
Not too far or the return spring pressure can cause the throttle plate to dig into the wall.