Idle speed adjustments are easily accomplished, but you must be
careful to perform them under the proper conditions. The engine must be fully
warmed up. The best procedure is to drive the vehicle for several miles after
the temperature gauge indicates that the coolant has reached operating
temperature. All normal operating conditions should be maintained. For example,
the air cleaner and all vacuum hoses should be installed or connected, the choke
should be wide open, and all accessories should be off. This includes the engine
cooling fan if it is electrical. If necessary, unplug it. Also, avoid extremes
of outside temperature, and replace a thermostat that makes the engine operate
too hot or too cold before proceeding.
Disconnect the air bypass solenoid connector when
checking idle speed on a 1987 626 below sea
level
Adjusting the idle speed on carbureted 323s-Carbureted
GLC and 626 models similar
Adjusting the idle speed on fuel injected 323
models-626 fuel injected models similar
On the 1978-79 GLC and 1979 626 models, disconnect the canister
purge hose between the canister and the air cleaner. On the 1986-87 626 and
MX-6, run the engine at 2,500-3,000 rpm in Neutral for three minutes before
proceeding.
Warm up the engine to normal operating temperature and turn off all
accessories.
Connect a reliable tachometer according to tool manufacturer's
instructions (usually between the coil negative (-) terminal and ground).
On 1987 626s only, disconnect the air bypass solenoid connector at
altitudes of less than 3,280 feet or 1,000 meters (sea level).
Note the idle speed. Compare this reading to the appropriate range in the
Tune-Up Specifications chart located in this section.
Read the tachometer's 4-cylinder scale, for both rotary and
piston engines. If the tachometer has only a 6-cylinder scale and an 8-cylinder
scale, read the 8-cylinder scale and multiply all readings by two to get the
correct rpm. For example, if the specified rpm is 700, set the idle speed at 350
rpm, as indicated on the 8-cylinder scale.
If the idle speed does not fall within the designated range, locate and
turn the appropriate idle speed adjusting screw until the desired reading is
attained:
On carburetor-equipped engines, the throttle adjusting screw is usually
located on the lower portion of the carburetor near the throttle valve
shaft. The screw acts directly on a flange which is integral with the
throttle shaft; it does not actuate any cams or levers.
On models equipped with electronic fuel injection, the air adjusting
screw is located on top of the throttle body.
On 1986-87 323s, after adjusting the idle speed, the dashpot must be
adjusted as follows:
Start the engine and warm it up to normal operating temperature.
With the tachometer still connected, increase the engine speed to 3,000
rpm, then slowly reduce the engine speed and make sure the dashpot rod
contacts the lever at 2,400-2,600 rpm.
If it does not operate as described, loosen the locknut and adjust the
rod by turning the dashpot.
On 1987 626s, fasten the air bypass solenoid connector, if applicable.
Disconnect and remove the tachometer.
626 DIESEL ENGINE
Adjusting the idle speed on the diesel requires you to have a
special tachometer which measures idle speed from a special sensor on the
injection pump.
Turn all of the vehicle's accessories to the off position, then connect a
diesel tachometer, according to the tool manufacturer's instructions.
Checking and adjusting accelerator cable deflection on
the 626 diesel
Adjust idle speed on the 626 diesel by (1) loosening
the locknut, then (2) turning the adjusting bolt
Place a ruler near the accelerator pedal and then depress the pedal to
determine the play in the cable. It should be 0.04-0.12 in. (1-3mm). If
necessary, lengthen the cable (to increase play) by loosening the nut on the
firewall side of the cable bracket and then tightening the nut on the other
side. You would shorten the cable, in order to decrease play, by reversing the
order in which the nuts are loosened.
Drive the car until several miles after the temperature gauge indicates
normal operating temperature, to warm up the engine. Measure the engine rpm
with the tachometer.
If the rpm is outside the range of 800-850 rpm, loosen the locknut on the
idle adjusting bolt on the injection pump. Then, turn the bolt clockwise to
increase the idle speed or counterclockwise to decrease it. Secure the
adjusting bolt with the locknut.
Disconnect and remove the tachometer.
1988-89 Models
The idle speed is controlled automatically by the Idle Speed
Control (ISC) solenoid valve, and adjustment is usually not necessary. However,
if rough idling occurs when pin 1 of the green test connector is grounded, then
adjustment of the idle speed is required. If adjustment is necessary, proceed as
follows:
Turn all of the vehicle's accessories to the off position, then connect a
tachometer to the engine check connector (see illustration).
Tachometer hooked up to the underhood check
connector-929 shown
Idle speed adjustment for the 929-other models
similar
Warm up the engine to normal operating temperature.
Ground pin 1 of the green test connector with a jumper wire. (An
illustration of this step is shown in the ignition timing portion of this
section.)
With the test connector grounded, check the idle speed. Compare this
reading to the Tune-Up Specifications chart located in this section. If it is
not within the specified range, remove the rubber cap from the air adjusting
screw on the throttle body and turn the screw to adjust the idle speed.
Once the idle speed is within specification, install the cap and
disconnect the jumper wire from the test connector.
On 1988 323s, after adjusting the idle speed, the dashpot must be adjusted
as follows:
Start the engine and warm it up to normal operating temperature.
With the tachometer still connected, increase the engine speed to 3,000
rpm, then slowly reduce the engine speed and make sure the dashpot rod
contacts the lever at 2,400-2,600 rpm.
If it does not operate as described, loosen the locknut and adjust the
rod by turning the dashpot.
Disconnect and remove the tachometer.
ROTARY ENGINES
Carbureted Vehicles
All 1979-83 RX-7s were equipped with a carburetor. 1984-85
RX-7s were equipped with either a carburetor (12A engine) or fuel injection (13B
engine).
If possible, set up an extra cooling fan to blow additional air into the
engine compartment.
Set the parking brake and block the wheels.
Switch all accessories to the off position.
Remove the fuel tank filler cap.
On 1979-83 models, disconnect and plug the hose at the idle compensator in
the air cleaner. On 1984-85 vehicles with a manual transmission, disconnect
the richer solenoid connector.
On 1981-83 models, make sure the throttle opener (if equipped
with air conditioning) and dashpot do not prevent the idle lever from returning
to the idle stop.
Connect a tachometer to the engine.
Start the engine and allow it to reach normal operating temperature. On
vehicles equipped with an automatic transmission, shift the selector lever to
the D (Drive) position.
Check the idle speed with the tachometer. (Read the tachometer as if
testing a conventional 4-cylinder engine.) If the idle speed is not correct,
adjust it by turning the throttle adjusting screw on the carburetor.
Read the tachometer's 4-cylinder scale, for both rotary and
piston engines. If the tachometer has only a 6-cylinder scale and an 8-cylinder
scale, read the 8-cylinder scale and multiply all readings by two to get the
correct rpm. For example, if the specified rpm is 700, set the idle speed at 350
rpm, as indicated on the 8-cylinder scale.
Unplug and reconnect the hose at the idle compensator on the air cleaner,
or secure the richer solenoid connector, if applicable. Install the fuel tank
filler cap.
After adjusting idle speed, the throttle sensor on the
carburetor should also be adjusted. For information on that procedure, please
refer toSection 5 of this manual.
Disconnect the tachometer and unblock the wheels.
Fuel Injected Vehicles
1984-85 RX-7
Switch all electrical accessories to the off position and remove the fuel
filler cap.
Start the engine and let it run until it reaches normal operating
temperature.
Use a pair of voltmeters or test lights to check the
throttle sensor setting-1984-85 fuel injected
RX-7
If necessary, turn the throttle sensor adjusting
screw-1984-85 fuel injected RX-7
Adjust idle speed by turning the
AAS
Check/adjust the throttle sensor by performing the following:
With the engine OFF, connect a pair of voltmeters to the green
check connector as shown in the illustration. If voltmeters are not
available, a dual set of test lights may be used instead.
Turn the ignition switch ONand check to see if current flows to
one of the voltmeters. When using the test light method, the light will
illuminate when current flows.
If there is no current, remove the rubber cap from the throttle sensor
screw and turn the screw clockwise only until current flow is indicated on
one of the voltmeters (or test lights). If both voltmeters show current,
remove the cap and turn the screw counterclockwise so that current flows to
only one voltmeter (or test light).
Install the rubber cap and disconnect the voltmeters.
Once the throttle sensor is adjusted, disconnect the vent and vacuum
solenoid connector.
Connect a tachometer, then start the engine.
Adjust the idle speed to 800 rpm by turning the Air Adjust Screw (AAS) on
the throttle body. After adjusting the idle speed, reinstall the blind cap
onto the AAS, if so equipped.
Shut off the engine, then attach the vent and vacuum solenoid connector.
Disconnect and remove the tachometer, then install the fuel tank filler cap.
1986-89 RX-7
Switch off all electrical accessories. Start the engine and let it run
until it reaches normal operating temperature, then shut off the engine.
Connect a jumper wire to the terminals of the initial set coupler.
Connect a tachometer to the service coupler at the trailing side coil with
igniter. If the tachometer does not function correctly, reconnect it at the
leading side coil with igniter (black coupler).
If using an inductive (secondary pick-up) type tachometer,
connect it only at the trailing side of the spark plug wires. If connected at
the leading side coil with igniter, it will not function properly.
Check/adjust the throttle sensor by performing the following:
With the engine OFF, connect dual checker lamps 49 F018 001 or
equivalent to the green check connector.
Turn the ignition switch to the ONposition and check that one of
the lamps illuminates.
If both lamps illuminate or neither one does, turn the throttle sensor
adjusting screw until only one of the lamps illuminates. If both of the
lamps illuminate, remove the rubber cap and turn the screw counterclockwise.
If neither lamp illuminates, turn the screw clockwise. Do not use excessive
pressure on the screw.
Remove the checker lamps and reinstall the rubber cap.
On 1986-89 non-turbo models, remove the blind cap from the throttle body
and adjust the idle speed by turning the Air Adjust Screw (AAS). On 1987-89
turbocharged models, remove the blind cap from the Bypass Air Control (BAC)
valve and adjust the idle speed by turning the AAS.
When adjustment is complete, shut the engine OFF, then disconnect
and remove the tachometer.
Connect a jumper wire to the terminals of the initial
set coupler-1986-89 RX-7
Connect a tachometer to the service coupler at the
trailing side coil with igniter-1986-89 RX-7
Use dual checker lamps to verify the throttle sensor
setting-1986-89 RX-7
If necessary, turn the throttle sensor adjusting
screw-1986-89 non-turbo RX-7
If necessary, turn the throttle sensor adjusting
screw-1986-89 turbocharged RX-7
Adjust the idle speed by turning the AAS on the
throttle body-1986-89 non-turbo RX-7
On turbocharged RX-7 models, the AAS is located on the
BAC valve
Install the blind cap and disconnect the jumper wire from the initial set
coupler.
Be sure to remove the jumper wire, otherwise engine performance
will be reduced.
Idle Mixture Adjustment
PISTON ENGINES
All 1978-82 Models; 1983 GLC Wagon and 1986-87 Carbureted 323
Idle mixture adjustment for all 1978-82 Mazda piston engine cars,
as well as 1983 GLC Wagons and 1986-87 carburetor-equipped 323s, requires the
use of an HC/CO analyzer. Since this is an extremely expensive piece of
equipment, the adjustment procedure is complex, and this adjustment is not
required as a part of ordinary maintenance, no procedures are included here.
This adjustment can, however, be checked at a reasonable cost at many diagnostic
centers, or may be checked during mandatory vehicle emission inspections, where
applicable. If the engine exhibits a rough idle and/or smoke, combined (in some
cases) with hesitation or poor running at low speeds, the idle mixture might be
at fault. First, check all the basic tune-up adjustments such as dwell, ignition
timing, and spark plug condition, and verify that there are no vacuum leaks due
to disconnected or leaking hoses. Then, if these symptoms persist, have the idle
mixture checked with an HC/CO meter at a dealer or diagnostic center.
If incorrect readings are detected, we suggest you take the
vehicle to a shop or dealer familiar with Mazdas and have the idle mixture
adjusted according to the procedure specified by the factory.
1983-85 GLC (Except Wagon) and 626 (Except Diesel)
The carburetor must be removed and disassembled to gain access
to the mixture screw since an idle mixture adjustment is normally only necessary
in the event of carburetor overhaul. For information on carburetor removal and
installation, please refer toSection 5 of this
manual.
The air/fuel mixture for most 1983-85 carbureted piston engine
models can readily be checked with a dwell/tachometer. An incorrect reading can
indicate either an improper idle mixture or a faulty oxygen sensor. Make sure
that the engine is properly tuned and that all vacuum hoses are properly
connected before suspecting an improper idle mixture.
Do not secure the spring pin (which locks the mixture adjusting
screw) until the adjustment has been performed.
To check/adjust the idle mixture:
On 1984 626s only, disconnect and plug the idle compensator, thermosensor,
and reed valve hoses.
Connect a tachometer to the engine.
Connect a dwell meter that can register up to 90 degrees (and which is
suitable for four-cylinder engines). Connect the meter's positive (+/red) lead
to terminal Y of the Air/Fuel (A/F) solenoid valve service connector, and the
negative (-/black) lead to the engine.
The mixture adjusting screw can be turned with a
screwdriver
A spring pin is used to lock the mixture adjusting
screw in place
Gently tap the spring pin into position after adjusting
the idle mixture
Warm up the engine to normal operating temperature and turn off all
accessories.
Make sure the idle speed meets the following specifications; adjust it (if
necessary), as described earlier in this section:
1983-85 manual transaxle GLC: 850 rpm in Neutral
1983-85 automatic transaxle GLC: 1,050 rpm in N (Neutral)
1983-85 manual transaxle 626: 750 rpm in Neutral
1983-85 automatic transaxle 626: 700 rpm in D (Drive)
With the engine running at the designated idle speed, note the reading on
the dwell meter; the reading should be 32-40 degrees.
If the dwell reading is not within the appropriate range, adjust the idle
mixture by turning the mixture adjusting screw, located near the base of the
carburetor.
Make sure that the idle speed still meets specifications.
Idle speed of the GLC with automatic transaxle should now be
checked with the gear selector in D (Drive), but MAKE SURE the parking brake is
set and the drive wheels are blocked. The correct reading is 750 rpm.
After the mixture is properly set, press in the spring pin to lock the
adjusting screw.
On 1984 626s only, unplug and reconnect the idle compensator,
thermosensor, and reed valve hoses.
Disconnect the dwell meter and tachometer. Re-attach the A/F solenoid
valve connector.
1986-89 Fuel Injected Models
On all 1986-89 fuel injected piston engine vehicles covered by
this manual, idle mixture is automatically maintained by the electronic engine
control unit, and thus, cannot be manually adjusted.
ROTARY ENGINES
Carbureted Vehicles
Most 1979-85 RX-7s were equipped with a carburetor.
Idle mixture adjustment is normally only necessary in the event
of carburetor overhaul. For information on carburetor removal and installation,
please refer toSection 5 of this manual.
Remove the throttle body, then cut out the idle limiter cap with a
hacksaw.
Assemble and install the carburetor. Be sure to install a new mixture
adjusting screw. Tighten it lightly until it seats, then turn it
counterclockwise three revolutions to attain the preliminary setting.
Connect a tachometer to the engine, then start the engine.
With the gear selector set to Neutral (or N), turn the throttle adjusting
screw to adjust the idle speed to 770 rpm (manual transmission) or 870 rpm
(automatic transmission). Read the tachometer as if testing a conventional
4-cylinder engine.
Set the idle speed to its highest rpm by turning the mixture adjusting
screw, located at the base of the carburetor.
With the gear selector still set to Neutral (or N), again turn the
throttle adjusting screw to adjust the idle speed to 770 rpm (manual
transmission) or 870 rpm (automatic transmission).
Turn the mixture adjusting screw clockwise to lower the idle speed to 750
rpm (manual transmission) or 840 rpm (automatic transmission).
CAUTION
When making adjustments with the engine running,
especially with the automatic transmission in drive, ALWAYS make sure the
parking brake is firmly set and the drive wheels are blocked in position.
On vehicles equipped with an automatic transmission, shift the selector
lever to the D position and adjust the idle speed to 750 rpm by turning the
throttle adjusting screw.
Shut the engine OFF.
Install a new idle limiter cap onto the mixture adjustment screw.
After adjusting idle speed, the throttle sensor on the
carburetor should also be adjusted. For information on that procedure, please
refer toSection 5 of this manual.
Disconnect and remove the tachometer.
Fuel Injected Vehicles
1984-85 RX-7
Idle mixture adjustment is normally only necessary when the
variable resistor is replaced. The variable resistor should be replaced when it
lacks continuity between terminals A and C or B and C, or whenever the engine is
replaced.
Switch all electrical accessories to the off position and remove the fuel
filler cap.
Connect a tachometer to the engine.
Check the variable resistor for continuity between
terminals A and C or B and C
Use a pair of voltmeters or test lights to check the
throttle sensor setting-1984-85 RX-7 with fuel
injection
If necessary, turn the throttle sensor adjusting
screw-1984-85 RX-7 with fuel injection
Start the engine and let it run until it reaches normal operating
temperature.
Check/adjust the throttle sensor, as described in the idle speed
adjustment procedure.
Disconnect the vent and vacuum solenoid valve connector.
Adjust the idle speed to 800 rpm by turning the Air Adjust Screw (AAS) on
the throttle body.
Set the idle speed to its highest rpm by turning the adjusting screw on
the variable resistor.
Once again, adjust the idle speed to 800 rpm by turning the Air Adjust
Screw (AAS) on the throttle body.
Adjust idle speed by turning the
AAS
Adjust the variable resistor with a
screwdriver
Turn the variable resistor adjusting screw counterclockwise until the
engine speed drops to 780 rpm, then turn it clockwise to reset the engine
speed to 800 rpm.
Shut the engine OFF.
Disconnect and remove the tachometer.
Reattach the vent and vacuum solenoid valve connector.
Fill the head of the variable resistor adjusting screw with an adhesive
agent (Part No. N304 23 795 or equivalent).
1986-89 RX-7
Idle mixture adjustment is normally only necessary when the
variable resistor is replaced. The variable resistor should be replaced if it
lacks continuity between terminals A and C or B and C, or whenever the engine is
replaced.
Connect a jumper wire to the terminals of the initial
set coupler-1986-89 RX-7
Connect a tachometer to the service coupler at the
trailing side coil with igniter-1986-89 RX-7
Use dual checker lamps to verify the throttle sensor
setting-1986-89 RX-7
If necessary, turn the throttle sensor adjusting
screw-1986-89 non-turbo RX-7
If necessary, turn the throttle sensor adjusting
screw-1986-89 turbocharged RX-7
Adjust the idle speed by turning the AAS on the
throttle body-1986-89 non-turbo RX-7
On turbocharged RX-7 models, the AAS is located on the
BAC valve
Switch all electrical accessories to the off position.
Start the engine and let it run until it reaches normal operating
temperature, then shut off the engine.
Connect a jumper wire to the terminals of the initial set coupler.
Connect a tachometer to the service coupler at the trailing side coil with
igniter. If the tachometer does not function correctly, reconnect it at the
leading side coil with igniter (black coupler).
If using an inductive (secondary pick-up) type tachometer,
connect it only at the trailing side of the spark plug wires. If connected at
the leading side coil with igniter, it will not function properly.
Check the variable resistor for continuity between
terminals A and C or B and C
Adjust the variable resistor with a
screwdriver
Check/adjust the throttle sensor, as described in the idle speed
adjustment procedure.
Remove the blind cap and adjust the idle speed to 750 rpm by turning the
Air Adjust Screw (AAS) on the throttle body.
Set the idle speed to its highest rpm by turning the adjusting screw on
the variable resistor.
Once again, adjust the idle speed to 750 rpm by turning the Air Adjust
Screw (AAS) on the throttle body.
Turn the variable resistor adjusting screw counterclockwise until the
engine speed drops to 730 rpm, then turn it clockwise to reset the engine
speed to 750 rpm.
Shut off the engine and disconnect the tachometer.
Install the blind cap and disconnect the jumper wire.
Be sure to remove the jumper wire, otherwise engine performance
will be reduced.
Fill the head of the variable resistor adjusting screw with an adhesive
agent (Part No. N304 23 795 or equivalent).
