1991 ACURA NSX Service Repair Manual

Throttle Bod y
Descriptio n
The throttl e bod y i s o f th e single-barre l side-draf t type .
The lowe r portio n o f th e throttl e valv e i s heate d b y
engin e coolan t whic h is fe d fro m th e cylinde r head . Th e
idl e adjustin g scre w whic h increases/decrease s bypas s
ai r an d th e evaporativ e emissio n (EVAP ) contro l
caniste r por t ar e locate d o n th e to p o f th e throttl e body .
A throttl e valv e dashpo t i s use d t o slo w th e throttl e
valv e a s i t approache s th e close d position .
THROTTL EVALVEDASHPO TCONTRO L THROTTL E
DIAPHRAG M STO P SCRE W
Inspectio n
CAUTION : D o no t adjus t th e throttl e sto p screw .
It i s prese t a t th e factory .
1. Star t th e engin e an d allo w i t t o reac h norma l
operatin g temperatur e (th e coolin g fa n come s on) .
2 . Disconnec t th e vacuu m hos e (t o th e EVA P contro l
canister ) fro m th e to p o f th e throttl e body ; connec t
a vacuu m gaug e t o th e throttl e body .
3 . Allo w th e engin e t o idl e an d chec k tha t th e gaug e
indicate s n o vacuum .
IDLE ADJUSTIN GSCREW(Non-adjustable )
TPSENSO R
THROTTL EACTUATO R
THROTTLEVALVE
ACCELERATO RPEDALANGL ESENSO R
VACUU M PUMP/GAUG EA973X–041 –XXXX X
If ther e is vacuum , chec k th e throttl e cabl e (se e
pag e 11-130 ).
4 . Chec k tha t vacuu m is indicate d o n th e gaug e whe n
th e throttl e i s opene d slightl y fro m idle .
I f th e gaug e indicate s n o vacuum , chec k th e
throttl e bod y port . I f th e throttl e bod y por t i s
clogged , clea n it wit h carbureto r cleaner .
5. Sto p th e engin e an d chec k tha t th e throttl e cabl e
operate s smoothl y withou t bindin g o r sticking .
I f ther e ar e an y abnormalitie s in th e abov e steps ,
chec k for :
Excessiv e wea r o r pla y i n th e throttl e valv e
shaft .
Stick y o r bindin g throttl e leve r a t ful l clos e
position .
Clearanc e betwee n throttl e sto p scre w an d
throttl e leve r a t ful l clos e position .
(cont'd )
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Intake Air System

There should be

no clearance.
Throttle Body (cont'd)

THROTTLE LEVER

THROTTLE STOP SCREW.

(Non-adjustable)

Replace the throttle body if there is excessive play in

the throttle valve shaft or if the shaft is binding or

sticking.

(cont'd)ProCarManuals.com

Throttle Bod y (cont'd )
Disassembl yTHROTTLECABLE
22 N· m(2.2 kg-m ,16lb-ft )
CAUTION :
THROTTL E
VALV E
DASHPO TTPSENSO R
CONTRO L
DIAPHRAG M
Testing, pag e 11-13 5
IDLE ADJUSTIN GSCREW
O-RINGReplac e
The throttl e sto p scre w i s non-adjustable .
Afte r reassembly , adjus t th e throttl e cabl e (se e pag e 11-130 ).
Afte r replacement , adjus t th e idl e spee d (se e pag e 11-102 ).
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Testing

1. Check the vacuum line for leaks, blockage or a
disconnected hose.

2. Disconnect the vacuum hose from the throttle valve dashpot control diaphragm, and connect a
vacuum pump to the hose.
THROTTLE
VALVE
DASHPOT

CONTROL
DIAPHRAGM 4. Connect a vacuum pump to the throttle valve
dashpot control diaphragm.
5. Apply vacuum and check that the rod pulls in and vacuum holds.
3. Apply vacuum and check the speed the vacuum goes out.
Vacuum should go out slowly.
VACUUM PUMP/GAUGE

A973X–041–XXXXX

THROTTLE
VALVE
DASHPOT
CHECK VALVE
If the vacuum holds or goes out quickly, replace
the throttle valve dashpot check valve and retest. If the vacuum does not hold or the rod does not
move, replace the throttle valve dashpot control
diaphragm and retest.ProCarManuals.com

Intake Air System

Description

Satisfactory power performance is achieved by closing and opening the intake air bypass (IAB) control valves. High tor-

que at low engine speed is achieved when the valves are closed, whereas high power at high engine speed is achieved

when the valves are opened.
Intake Air Bypass (IAB) Control System

OPEN: HIGH ENGINE SPEED
INTAKE AIR BYPASS (IAB) CONTROL

SOLENOID VALVE ON

IAB

CHECK

VALVE

CLOSE: LOW ENGINE SPEED

IAB

CONTROL

DIAPHRAGM

IAB

CONTROL

VALVE
ECM
IAB

VACUUM

TANK
IAB CONTROL

SOLENOID

VALVE

TO No. 2 (15 A) FUSE
BLK/YEL

RED/BLUProCarManuals.com

Intake Ai r Bypas s (IAB ) Contro l Valv e Testin g
CAUTION : D o no t adjus t th e IA B contro l valv e full -
clos e screw . I t wa s prese t a t th e factory .
1. Chec k th e IA B contro l valv e shaf t fo r bindin g o r
sticking .
2 . Chec k th e IA B contro l valv e fo r smoot h movement .
3. Chec k tha t o f th e IA B contro l valv e is i n clos e
contac t wit h th e stoppe r whe n th e vacuu m hos e is
disconnecte d fro m th e IA B contro l diaphragm .
STOPPER
4. Chec k tha t o f th e IA B contro l valv e is i n clos e
contac t wit h th e full-clos e scre w whe n yo u appl y
38 0 m m H g ( 1 5 in . Hg ) o f vacuu m to th e IA B con -
tro l diaphragm .
I f an y faul t i s found , clea n th e linkag e an d shaft s
wit h carbureto r cleaner .
FULL-CLOS E
SCRE W
If th e proble m stil l exist s afte r cleaning ,
disassembl e th e intak e manifol d an d chec k th e
IA B valv e bod y assembl y (se e pag e 11-140 ).
(cont'd )
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Intake Air System
Intake Air Bypass (IAB) Control System (cont'd)

Disassembly

22 N.
m (2.2 kg-m, 16 Ib-ft)
INTAKE MANIFOLD 22 N.
m (2.2 kg-m. 16 Ib-ft)

GASKET
Replace.

WASHER
Replace.
22 N.
m (2.2 kg-m, 16 Ib-ft)

GASKET

Replace.

CHAMBER

ICM

IAB VALVE
BODY

ASSEMBLY
GASKET

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