Rough Idle - Always - Mazda MX-5 1990 Workshop Manual

F
TROUBLESHOOTING GUIDE
8
ROUGH IDLE - ALWAYS
DESCRIP· • Engine vibrates excessively at idle in every condition
TION
[TROUBLESHOOTING HINTS]
CD
Air/Fuel mixture too lean
• Air leakage
• Fuel injection control malfunction
• Low fuel line pressure
@ One or more injectors not operating or clogged
STEP INSPECTION
@ One or more spark plugs not sparking
@
Injection timing misadjustment
®
Low engine compression
ACTION
Check for correct intake manifold vacuum at idle Yes Go to next step
Vacuum: More than 450 mmHg (17.7 inHg)
2 Check if air cleaner element is clean
c::::r page F-75
3 Check if "00" is displayed on Self-Diagnosis
Checker with ignition switch ON
c:::r page F-78
4
Check switches for correct operation with Self-
Diagnosis Checker Monitor Lamp and ignition
switch ON
5 Check if ECU terminal voltages are OK
(20, 20 and 2Q)
No Check for air leakage of intake air sys-
tem components
c::::t
page F-93
Yes Go to next step
No Replace air cleaner element
Yes Go to next step
No Malfunction Code No. displayed
Check for cause (Refer to specified
check sequence)
"88" flashes
Check ECU terminal 1 F voltage
Voltage: Approx. 12V
(Ignition switch ON)
c:::r page F-92
c::J
page F-80
c::J
page F-128
q
If OK, replace ECU
c::::t
page F-127
q
If not OK, check wiring between
ECU and Self-Diagnosis Checker
c::J
page F-7
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
L7'
page F-90
and Self-Diagnosis Checker c:::r page F-7
Yes Go to next step
c::J
page F-129 No Check for cause (Refer to "Check Point
for Each Terminal") c:::r page F-132
F-30