Rough Idle Just After Starting - Mazda MX-5 1990 Workshop Manual

TROUBLESHOOTING GlllDE
13
ROUGH IDLE JUST AFTER STARTING
DESCRIP-
TION
• Engine starts normally but vibrates excessively just after starting
[TROUBLESHOOTING HINTS]
CD
Fuel injection control and idle speed control malfunction
• Start signal not input to ECU
STEP
INSPECTION
®
Idle speed misadjustment
@
Ignition timing misadjustment
ACTION
Check if "00" is displayed on Self-Diagnosis Yes Go to next step
Checker with ignition switch ON
c::::r page F-78 No
Malfunction Code No. displayed
Check for cause (Refer to specified
check sequence)
~
SYSTEM SELECT 1
TEST SW
,~...a:::=:fm~SELF
TEST
(;%;.~~
2 Check switches for correct operation with Self-
Diagnosis Checker Monitor Lamp and ignition
switch ON
c:::r page F-89
SELECT SW A
"88" flashes
Check ECU terminal 1 F voltage
Voltage: Approx. 12V
(Ignition switch ON)
¢
If OK, replace ECU
~ 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 1 D
F
u
page F-80
c::7
page F-128
c:::r page F-127
c::7
page F-7
c:::r page F-90
and Self-Diagnosis Checker c::::r page F-7
3
Check if ECU terminal 1 C voltage is OK Yes Go to next step
a
page F-128
Voltage: Approx. 10V (While cranking)
No Check for cause (Refer to "Check Point
for Each Terminal")
u
page F-131
4
Check for correct ignition timing at idle
Yes Check for correct idle speed c:::r page F-76
u
page F-75
Idle speed: 850 ± 50 rpm
Ignition timing: 10 0
±
1 0 BTDC
¢
If OK, go to next step
c:::;>
If not OK, adjust idle speed
u
page F-76
GND TEN
~
No
Adjust c:::r page F-75
5 Try known good ECU and check if condition
improves
c:::r page F-127
05UOFX-030
F-39