Low Idle Speed/Rough Idle - Before Warm-Up - Mazda MX-5 1990 Workshop Manual

F
TROUBLESHOOTING GUIDE
9
LOW IDLE SPEED/ROUGH IDLE - BEFORE WARM-UP
DESCRIP-
TION
• Engine speed low or engine vibrates excessively at idle during warm-up
[TROUBLESHOOTING HINTS]
CD
Low intake air amount
• Airflow meter stuck
• Air cleaner element clogged
• Idle speed control
[
Air valve ]
Correction for coolant temperature
STEP
INSPECTION
Check if "00" is displayed on Self-Diagnosis
Checker with ignition switch ON
L7
page F-7B
2 Check switches for correct operation with Self-
Diagnosis Checker Monitor Lamp and ignition
switch ON
CT
page F-89
3
Check if ECU terminal voltages are OK
(20, 20 and 20)
c:::r
page F-129
4
Check for correct intake manifold vacuum at idle
5
Check if air cleaner element is clean
CT
page F-75
F-32
~
Low fuel injection amount
• Fuel injection control malfunction
(Correction for coolant temperature)
@
Poor atomization of fuel
• Low RVP (summer) fuel used in cold weather
ACTION
Yes Go to next step
No Malfunction Code No. displayed
Check for cause (Refer to specified
check sequence)
"BB" flashes
Check ECU terminal 1 F voltage
Voltage: Approx. 12V
(Ignition switch ON)
=>
If OK, replace ECU
9
If not OK, check wiring between
ECU and Self-Diagnosis Checker
Yes Go to next step
No Lamp not ON/OFF with specified
switch
Check for cause (Refer to specified
check sequence)
Lamp always ON
Check wiring between ECU terminal 10
L7
page F-80
c::::r page F-128
c:::r page
F-127
L7
page F-7
CT
page F-90
and Self-Diagnosis Checker
c:::r
page F-7
Yes Go to next step
No Check for cause (Refer to "Check Point
for Each Terminal")
c:::r page
F-132
Yes Go to next step
No Check for air leakage of intake air sys-
tem components
c:::::r page F-93
Yes Go next step
No Replace air cleaner element
c:::r
page F-92