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

F
TROUBLESHOOTING GUIDE
LOW IDLE SPEED/ROUGH IDLE - AFTER WARM-UP
• Engine runs normally at idle during warm-up but vibrates excessively after warm-up
[TROUBLESHOOTING HINTS]
CD
Idle speed control malfunction
W
Air/Fuel mixture too lean
• Air leakage of intake air system
• Low fuel line pressure
STEP
INSPECTION
2
Check if "00" is displayed on Self-Diagnosis
Checker with ignition switch ON
c::::r page F-78
Check switches for correct operation with Self-
Diagnosis Checker Monitor Lamp and ignition
switch ON
@
Air/Fuel mixture too rich
• Fuel injection control malfunction
(Correction for coolant temperature)
@
Poor ignition spark
®
Low engine compression "
ACTION
Yes Go to next step
No Malfunction Code No. displayed
Check for cause (Refer to specified
check sequence)
Yes
No
"88" flashes
Check ECU terminal 1 F voltage
Voltage: Approx. 12V
(Ignition switch ON)
c:::t>
If OK, replace ECU
c::>
If not OK, check wiring between
ECU and Self-Diagnosis Checker
Go to next step
Lamp not ON/OFF with specified
switch
Check for cause (Refer to specified
c::::r page F-80
c:r page F-129
c::r
page F-127
c::::r page F-7
c:::r page F-89
SYSTEM SELECT 1
TE"ST SW
SELF TEST
check sequence) c:::r page F-90
MONITOR
LAMP
A~/"\\'/~
3 Disconnect ISC valve connector at idle and
check if "clicking" is heard from ISC valve
Lamp always ON
Check wiring between ECU terminal
1
D
and Self-Diagnosis Checker
c::r
page
F-7
Yes Go to next step
No Replace ISC valve c:::r page F-99
4 Check for correct intake manifold vacuum at idle Yes Go to next step
Vacuum: More than 450 mmHg (17.7 inHg)
No Low vacuum
Check for air leakage of intake air sys-
tem components
c::r
page F-93
F-34