1991 ACURA NSX Service Repair Manual

Idle Contro l Syste m
Automati c Transaxl e (A/T ) Gea r Positio n Signa l
(From pag e 11-121 )
Chec k fo r a n ope n in th e wire :
1 . Tur n th e ignitio n switc h OFF .
2. Reconnec t th e 30 P (C412 ) con -necto r t o th e gaug e assembly .
3 . Reconnec t th e 26 P connecto r
to th e TCM .4. Star t th e engine .
5 . Measur e voltag e betwee n EC M
connecto r terminal s B 4 an d
A26 wit h th e transmissio n i nposition . EC
M CONNECTOR S
WIR E SID E O F FEMAL E TERMINAL S
I s ther e les s tha n 1. 0 V ? —
Repai r ope n i n th e wir e
betwee n th e EC M (B4 ) an d th e
gaug e assembly .— Repai r ope n i n GR N wir e
betwee n th e gaug e assembl y
an d th e A/ T gea r positio n
switch .
Chec k fo r a n ope n in th e wire :
Measur e voltag e betwee n EC M
Connecto r terminal s 8 4 an d A2 6
with th e transmissio n i n posi -tion.
Is ther e les s tha n 1. 0 V ? Repai
r ope n i n GRN/WH T wir e
betwee n th e gaug e assembl y an d
th e A/ T gea r positio n switch .
A/ T gea r positio n signa l i s OK .
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Neutral Switc h Signa l (M/T )
This signal s th e EC M whe n th e transmissio n i s i n neutral .
Inspectio n o f neutra l switc h signal .
Chec k fo r a n ope n in th e circuit :
1 . Tur n th e ignitio n switc h O N (II) .
2 . Measur e voltag e betwee n EC M
connecto r terminal s B 4 an d
A26 .
Is ther e voltage ?
Chec k fo r a shor t i n th e circuit :
1 . Shif t transmissio n int o gear .
2 . Measur e voltag e betwee n EC M
connecto r terminal s B 4 an d
A26 .
Is ther e approx . 5 V ?
Neutra l switc h signa l i s OK . EC
M CONNECTOR S
Chec k fo r a n ope n in th e wire :
1 . Tur n th e ignitio n switc h OFF .
2 . Disconnec t th e 3 P connecto r
fro m th e neutra l switch .
3 . Connec t neutra l switc h con -
necto r terminal s No . 1 to No . 3 .
4 . Tur n th e ignitio n switc h O N (II) .
5 . Measur e voltag e betwee n EC M
connecto r terminal s B 4 an d
A26 .
WIR E SID E O F FEMAL E TERMINAL S
WIR E SID E O F FEMAL E TERMINAL S
I s ther e voltage ? Replac
e th e neutra l switc h (se e
sectio n 13 ).
Repai r ope n i n th e wir e
betwee n th e EC M (B4 ) an d
th e neutra l switch .
Repai r ope n i n BL K wir e
betwee n th e neutra l switc h
an d G10 1 (locate d a t righ t mid -
dl e o f engine) .
Chec k fo r a shor t i n th e wire :
1 . Tur n th e ignitio n switc h OFF .
2 . Disconnec t th e EC M connec -
to r B (16P ) fro m th e ECM .
3 . Disconnec t th e 3 P connecto r
fro m th e neutra l switch .
4 . Chec k fo r continuit y betwee n
EC M connecto r termina l B 4
an d bod y ground .
I s ther e continuity ? Repai
r shor t i n th e wir e betwee n
th e EC M (B4 ) an d th e neutra l
switch .
Replac e neutra l switc h (se e
sectio n 13 ).
Substitut e a known-goo d EC M
an d recheck . I f prescribe d volt -
ag e i s no w available , replac e
th e origina l ECM . NEUTRA
L SWITC H 3 P CONNECTO R
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Idle Contro l Syste m
Clutch Switc h Signa l (M/T )
This signal s th e EC M whe n th e clutc h is engaged .
Inspection o f clutc h switc h signal .
Chec k fo r a n ope n in th e circuit :
1. Tur n th e ignitio n switc h O N (II) .2. Measur e voltag e betwee n EC M
connecto r terminal s C 4 an d
A26.
Is voltag e les s tha n 1. 0 V ?
Chec k fo r shor t i n th e circuit :
1 . Depres s th e clutc h pedal .
2 . Measur e voltag e betwee n EC M
connecto r terminal s C 4 an d
A26.
(To pag e 11-125 ) EC
M CONNECTOR S
Chec k th e clutc h switch :
1. Tur n th e ignitio n switc h OFF .2. Disconnec t th e 3 P connecto r
fro m th e clutc h switch .
3 . Chec k fo r continuit y betwee n
th e clutc h switc h connecto r
terminal s No . 1 an d No . 3 . WIR
E SID E O F FEMAL E TERMINAL S
CLUTC H SWITC H 3 P CONNECTO R
TERMINA L SID E O F MAL E TERMINAL S
I s ther e continuity ? —
Adjus t th e clutc h switch .
— Replac e th e clutc h switch .
CLUTC H SWITC H 3 P CONNECTO R
WIR E SID E O F FEMAL E TERMINAL S
I s ther e approx . 5 V ? Repai
r ope n i n th e wir e betwee n
th e EC M (C4 ) an d th e clutc h
switch .
Repai r ope n in BL K wir e betwee n
th e clutc h switc h an d G40 1
(locate d behin d lef t kic k panel) .
Chec
k fo r a n ope n in th e wire :
1. Tur n th e ignitio n switc h O N (II) .2. Measur e voltag e betwee n th e
clutc h switc h connecto r termi -
nal No . 1 an d bod y ground .
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(From pag e 11-124 )
Is ther e approx . 5 V ? EC
M CONNECTOR S
Chec k th e clutc h switch :
1 . Tur n th e ignitio n switc h OFF :
2 . Disconnec t th e 3 P connecto r
fro m th e clutc h switch .
3 . Tur n th e ignitio n switc h O N (II) .
4 . Measur e voltag e betwee n EC M
connecto r terminal s C 4 an d
A26 wit h th e clutc h peda ldepressed .
Is ther e approx . 5 V ? WIR
E SID E O F FEMAL E TERMINAL S
Replac e th e clutc h switch .
Repai r shor t i n th e wir e betwee n
th e EC M (C4 ) an d th e clutc h
switch .
Clutc
h switc h signa l i s OK .
Check fo r a shor t i n th e wire :
1 . Tur n th e ignitio n switc h OFF .
2 . Disconnec t th e EC M connec -
to r C (12P ) fro m th e ECM .
3 . Chec k fo r continuit y betwee n
EC M connecto r termina l C 4
an d bod y ground .
I s ther e continuity ?
Substitut e a known-goo d EC M
an d recheck . I f prescribe d voltag e
i s no w available , replac e th e orig -
ina l ECM .
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Idle Contro l Syste m
Brake Switc h Signa l
This signal s th e EC M whe n th e brak e peda l i s depressed .
Are th e brak e light s o n withou tdepressin g th e brak e pedal ?Inspec t th e brak e switc h (se e
sectio n 19 ).
Depres s th e brak e pedal .
D o th e brak e light s com e on ?
Is th e fus e OK ?
Chec k fo r a n ope n in th e wire :
1 . Depres s th e brak e pedal .
2 . Measur e voltag e betwee n
EC M connecto r terminal s F1 6
an d A2 6 wit h th e brak e peda l
depressed . —
Repai r shor t i n th e wir e
betwee n th e brak e switc h
an d th e BRAK E LIGH T S W
HOR N (2 0 A ) fuse .
— Replac e th e BRAK E LIGH T
S W HOR N (2 0 A ) fuse .
WIR E SID E O F FEMAL E TERMINAL S
I s ther e batter y voltage ? Repai
r ope n i n th e wir e betwee n
th e EC M (F16 ) an d th e brak e
switch .
Inspectio
n o f Brak e Switc h Signal .
Inspect th e BRAK E LIGH T S W
HORN (20 A ) fus e i n th e under -
hood fuse/rela y box .
Repai r ope n i n th e wir e
betwee n th e brak e switc h
an d th e BRAK E LIGH T S W
HOR N (2 0 A ) fuse .
Inspec t th e brak e switc h (se e
sectio n 19 ).
ECM CONNECTOR S
Brak e switc h signa l i s OK .
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Starter Switch Signal

This signals the ECM when the engine is cranking.

Inspection of Starter Switch Sig-

nal.
NOTE:

• M/T: Clutch pedal must be depressed.

• A/T: Transmission in position.

ECM CONNECTORS

Measure voltage between ECM

connector terminals C6 and A26

with the ignition switch in the

start position.

WIRE SIDE OF FEMALE TERMINALS

Is there battery voltage?

Is the fuse OK?
Repair short in the wire

between the ECM (C6) and

the No. 7 STARTER SIGNAL

(7.5 A) fuse or the PGM-FI

main relay.

Replace the No. 7 STARTER

SIGNAL (7.5 A) fuse.
Starter switch signal is OK.

Repair open in the wire between

the ECM
(C6)
and the No. 7

STARTER SIGNAL (7.5 A) fuse.
Inspect the No. 7 STARTER SIG-

NAL (7.5 A) fuse in the under-

dash fuse box.ProCarManuals.com

Idle Contro l Syste m
Idle Spee d Settin g
Inspection/Adjustmen t
NOTE: Befor e settin g th e idl e speed , chec k th e followin g
items :
— Th e Chec k Engin e ligh t ha s no t bee n reporte d on .
— Ignitio n timin g
— Spar k plug s
— Ai r cleane r
— PC V syste m
1 . Star t th e engine . Hol d th e engin e a t 3,00 0 rp m wit h
no loa d (A/ T in position , M/ T in neutral ) unti l
th e radiato r fa n come s on , the n tur n th e ignitio n
switc h OFF .
2 . Connec t th e SC S servic e connecto r t o servic e chec k
connector .
3. Connec t a OBDI I sca n too l (se e pag e 11-38 ) o r
tachometer .
• Connec t a tachomete r t o loo p o f ignite r uni t sec -
ondary , or.. .
TACHOMETE R
Remove th e rubbe r ca p fro m th e tachomete r
connector an d connec t a tachometer .
TACHOMETE R
RUBBERCAP
TACHOMETE RCONNECTOR
4. Restar t th e engine .
5 . Chec k idlin g i n no-loa d condition s i n whic h th e
headlights , blowe r fan , rea r defogger , coolin g fan ,
an d ai r conditione r ar e no t operating .
NOTE : D o no t depres s th e accelerato r peda l i n thi s
step .
Idl e spee d shoul d be :
Adjus t th e idl e speed , i f necessary , b y turnin g th e
idl e adjustin g screw .
NOTE : Afte r adjustin g th e idl e spee d i n thi s step ,
chec k th e ignitio n timin g (se e sectio n 23 ).
I f i t i s ou t o f spec , g o bac k t o ste p 4 .
IDL E ADJUSTIN GSCREW
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6. Disconnect the SCS service connector.

7. Depress the accelerator pedal and stabilize the

engine speed at 1,000 rpm, then slowly release the

pedal until the engine idles, then check the idle

speed.

Idle speed should be:ProCarManuals.com