- Car Care & Maintenance
Where is the Idle Air Adjustment Screw on a 1991-94 Mercury Capri?
Before 1980, adjusting the engine idle usually meant adjust the idle screw and mixture screws located on the base of carburetor. Since the 1980s, all cars are fuel injected and the car computer controls the fuel mixture. But even into the 1990s, car idle could manually be adjusted. First, car idle is when you are not driving, as soon as you start moving, you are no longer idling.
Car idle when the engine is cold is always faster, usually by another 500 RPMs, so in a 1991-94 Mercury Capri, the standard idle when the engine is warm or hot is between 800-900 RPMs, when cold, it is around 1500 or so. Once the engine warms, it will automatically drop to spec. All four cylinder engines idle at much higher RPMs than six or eight cylinder engines, which usually idle at 500-700 RPM.
To adjust the air idle in a Mercury Capri, to the following:
1. Make sure engine timing is per spec.
2. Turn off all electrical loads.
3. Make sure the fan control is OFF.
4. Warm up engine to 175 F.
5. Attach a RPM tester to Pin 1 (white) of the STI connector.
6. Refer to RPMs of engine.
7. Use a screwdriver to turn the Idle Air Screw (as shown) until the idle is 850-900 RPM. Clockwise decreases RPM.
If you have a vacuum leak undetected, you will not be able to adjust the RPMs very well until fixed. It may make the engine rev too high or too low..