Transcript
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CURING ERRATIC IDLE (Part 1)
eneral:
ratic idle is one of the most common
oblems with our cars. This is caused by the
umber of engine components that are
fecting it, such as: IAA (Idle Air Adjusting
nit), Air Regulator, Throttle Bodies, Injectors,
AS, fuel delivery, vacuum piping...
his article will cover the three components
entioned first.
AA-unit:
his unit consists mainly of two valves: FICD
d AAC. The FICD valve compensates for
PM drop when AC compressor is activated.
he symptoms of the FICD failing are idle
op and vibrations when switching on the air
ndition.
he AAC (Auxiliary Air Control) valve is
ntrolled by the ECU (PWM-control) to sete idle speed to a pre-programmed level. The
CU switches the AAC on and off very fast
d thereby is able obtain a gradual opening of
e valve. The AAC opening ratio can be
bserved on a Techtom MDM-100. If the valve
completely closed at idle it could mean that
e idle screw is not adjusted correctly (too
uch air enters through it) or there is a vacuum
ak (could be dirty TB's not closing all theay).
ery often is the IAA unit (pic 1.) diagnosed
ulty and replaced. Since it costs ~$200 it's
orth to take the time and fix it yourself. Just
long as the solenoids are electrically intact
ere's not much that can go wrong with this
1.
2.
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nit.
rst off, check the solenoid resistance (don't
rget to clean the connectors too).
CD => ~22 Ohm
AC => ~10 Ohm
ou can also check the solenoid operation by
plying 12V from the battery to its connectors
ou should hear a click).the resistance is far off then you really need
new IAA-unit, if not then read on...
emove the IAA from the plenum. It's attached
it with 4 screws. There is also a gasket
tween the IAA and the plenum. I reused the
d one since it wasn't broken. Disassemble the
lenoids as in picture 2. Check if the spring
side them is not broken.ow clean the solenoids and the IAA-unit
sing with WD-40 or Brake Cleaner or
milar.
eassemble and it's as good as new.
ir Regulator:
he purpose of the air regulator is to raise the
le during engine warm-up by letting
ditional air to enter the intake.he symptoms of the air regulator going bad is
ther low unstable idle during warm up or
nstantly high idle.
he regulator consists of a bimetal-activated
utter that closes after ~5 min of engine
peration and cuts off the airflow.
ote: It's normal that the shutter is only
rtially open at room temperature.
heck the resistance between the pins in the
nnector. It should be ~75 Ohm. If not good
en replace the whole regulator.
nother problem could be that the regulator is
ogged, causing the shutter to stick.
he air regulator is located on the rear of the
enum and is attached to it with 2 screws.
here are 4 screws keeping the housing
3.
4.
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gether. Remove them and clean the regulator
ternals (pic 3).
hrottle Bodies (TB's):
irty throttle bodies can be the cause of
nstable idle and hesitation.
emove the rubber hoses attached to them. It's
siest when the hoses are warm as it makesem softer. Twist them and pull (push them
rther on to the intercooler pipe too). Detach
so the small hoses beneath the TB's.
se an appropriate detergent to clean the TB
ternals. I've found Brake Cleaner and WD-40
work well. Use a toothbrush to scrub on the
rface.
ry and reassemble.
ome people reported that after cleaning the
B's they had to reset the ECU to get the idle
eed down. I would suggest disconnecting the
gative battery terminal before you start
eaning the TB's. It takes ~30 minutes for the
CU to forget what it has learned and that is
ow long it will take (at least...) to clean the
B's.
fter cleaning the TB's the idle may need to be
adjusted as the amount of air entering the
enum may have changed (depending on how
rty the TB's were). Adjust the Throttle
osition Sensor first (see Part 2) and then
just the idle as described below.
le adjustment:
ormally the engine should idle at ~800RPM.it's to high then you should try to adjust it.
et the engine warm up to normal operating
mperature. Put the transmission in neutral
ar.
isconnect the connector on the AAC valve
ic 2).
ith the idle screw (pic 1) adjust the idle
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cording to the values listed for the different
models:
A AT = 720 RPM
A MT => 650 RPM
T => 700 RPM
econnect the AAC and you should hear the
gine rev up ~50RPM. That means that AACworking correctly and the ECU has control
ver the idle speed now.
MPORTANT! The purpose of the idle screw
to set the bottom value of the idle and let the
CU control it. If you adjust the screw for
gher idle than the above then the ECU is no
nger in charge of the idle speed.
you've got a Techtom MDM-100 then the
le adjustment is easier.
et the engine warm up fully and watch the
AC opening on the MDM while you're
justing the idle screw. Adjust it so that the
AC is 15%-20% open.
you're not able to reach the 15% and the
DM shows a value below that even with the
le screw fully in then you've got a bigcuum leak somewhere (see how to find it
ERE).
CURING ERRATIC IDLE (Part 2)
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eneral:
his part describes further investigation on
nstable idle problems.
ain topics are Coolant Temp sensor, TPS,
ower balance test, Ignition Coils, Spark plugs,
jectors, CAS, MAS, Fuel delivery, PCVs,
cuum leaks and compression test.
oolant temperature sensor:
he ECU coolant temp sensor is a very
mmon cause of high idle, hesitation and
fety boost mode.
s located in front of the engine on the upper
uminum coolant pipe (see pic 1).
ost often the source of the problem is bad
nnection caused by corrosion on its contactee Connector Cleaning document for the
eaning procedure).
ou can also check the resistance of the sensor
y measuring it acrossits terminals.
he resistance should be:
1-2.9 kOhm at 20C (68F)
68-1.0 kOhm at 50C (122F)
30-0.33 kOhm at 80C (176F)
PS - Throttle Position Sensor:
oorly adjusted TPS can cause jumping or high
le. The TPS is located on the left throttle
ody, pic 2.
o measure its output voltage (if you haven't
ot a AVC-R or AFC or a Techtom MDM-
00) you have to insert a thin wire in its
rness contact (pic 2), since it has to be
nnected while measuring.easure between the middle pin and the
assis or battery ground.
he voltage should be between 0.4V and
45V (the spec says 0.5V but that's to high
om my experience).
o adjust the voltage, turn ignition switch ON,
osen the screws holding the TPS and turn it
ghtly (CW => -) until the voltage is within
1.
2.
3.
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ec. Tighten the screws and recheck voltage.
pen the throttle fully and check that the
utput voltage is ~4V.
mportant: If you haven't cleaned the throttle
odies, do it first (seePart1) and then adjust the
PS.
worn out TPS can cause problems like:
mping RPM while driving and shifting
oblems with auto transmission.
new TPS costs ~$29. Check the part number
ERE starting at page 2-A-8, section Throttle
hamber.
ower Balance test:
the engine is missing at idle, try to determine
the problem is connected to one of the
linders.
art the engine and proceed to disconnect each
the coil connectors (pic 3), one at a time.
he idle should drop when disconnecting a
il. If the idle doesn't change at all or changes
nly slightly compared to other cylinders then
ou've narrowed the problem to a single
linder.
nition Coils:
asiest way of checking a coil is to swap it
ith another good one.
you discovered one faulty cylinder in the
ower balance test then swap the suspected
il with a coil from a cylinder that was firing
rrectly. Perform the power balance test again
d see if the problem moves together with the
il. If yes then replace the coil.
ou can also check the resistance between the
iddle and the left pin (looking from the side
the engine) of the coil connector. It should
~0.7 Ohm.
4.
5.
6.
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heck also the coil connectors for corrosion
d overall condition. The locking pin tends to
ake and the connector can come off by itself.
ee Contact cleaning document for more info
n repairing the harness.
park plugs:
xamine all the spark plugs carefully causeey've got a lot to "tell".
e sure to know which one comes from which
linder. If you installed spark plugs that are to
ld then they could foul and contribute to an
nstable idle. Use the colder PFR6B-11B plugs
n a modded Z. Going one grade colder to
FR7B-11 is only necessary when pushing
ERIOUS power while racing. The standard
p is 1.1mm. The gap should be lowered onodified engines. I'm running on ~0.8mm gap.
ompare all the spark plugs to see if you've got
problem with one of the cylinders. If one
ark plug is abnormally fouled that could
ean that one injector is leaking. If there is an
l leak in the system (e.g. from a turbo) then
ou would see some burned oil residue on the
ug.
normal plug will be clean with white or tansulator. See www.ngksparkplugs.comfor
ore info on plugs.
jectors:
jectors themselves are hard to diagnose. Like
entioned above, a leaking injector could be
agnosed by looking at the spark plug. There
also one more hint that I've heard of. If you
t the car sit for a couple of hours and thenmove the plug then you would smell a strong
el smell from the cylinder that has a leaking
jector and the plug would probably be wet
ith fuel.
ou can also examine if the injector is
cking" if you let the car idle and put a long
rewdriver on the top of the injector while
utting your ear to the handle. You should hear
7.
8.
9.
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oud clicking. Compare the sound from all
e injectors. If an injector is not clicking then
s dead.
ou can check the resistance of the injectors as
ell by measuring it across its terminals. It
ould be between 10 and 14 Ohm.
ost often though, the problem is caused byrroded injector connectors. They are
cessible from the top of the plenum (pic 4).
they are broken or in a really bad shape then
would recommend that you replace them.
ou can use two sets of injector connectors
N: 24079-25P26 (~$20).They are meant for a
from the 80's but they'll fit, well almost...
ou will have
knock off a plastic pin on the injectornnector, not to difficult. See the Connector
eaning document for more info on this.
AS:
he Crank Angle Sensor informs the ECU
out the current position of the crank shaft
ic 5).
he most common reason for it affecting the
le is the connector getting dirty, although if e CAS connection is completely broken the
r won't start at all. The best way to examine
AS is to pull it out completely. Be sure to
ark its position so you can reinstall it like it
as before use millimeter precision here).
ean the connector if required. Check also
at the sensor is spinning freely without the
arings making to much noise and vibrations.
heck that the half circle pin inside its shaft istact. Some early model Zs had wrongly
achined heads causing the pin to wear out.
he ECU will not always report an error on the
AS. I had to put the ECU in test mode and
en crank the engine before the CAS-fault
de showed up.
10.
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AS:
ass Airflow Sensor (pic 6) tells the ECU how
uch air is entering the engine which in turn
ves the information about how much fuel
eds to be supplied.
heck the MAS by looking through it to see if
e hot-wire is damaged or clogged by dirt.
ou can gently clean the hot-wire by spraying
with a contact cleaner that doesn't leave a
otective film. I cleaned mine with brake
eaner since it evaporates completely but it
uld be a little harsh for the vulnerable hot
ire..
ever remove the mash screen! It serves both
a protection and has its effect on the airflow.
ou can check the MAS voltage at the ECUee ECU contact diagram) with a volt meter.
should read ~0.8V with ignition on (some
ople get 0.08V on the Techtom) and ~1.5V
idle, unless you've got a vacuum leak
mewhere...
acuum leaks:
asically examine all of the hoses for leaks. If
ere is a vacuum leak somewhere then air
at's not registered by MAS will enter the
stem causing the engine to run to lean.
ee the Finding Vacuum Leaks article for more
fo.
uel delivery:
heck the fuel pressure after the fuel filter.epressurize the fuel system by disconnecting
e fuel pump under the spare tire or
sconnecting the
el pump relay (see pic 7). Start the engine
d let it stall. Crank it again a couple of times
let more fuel out.
here's always a bit of pressure left in the
oses so have some rags handy.
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isconnect the fuel filter hose from the metal
pe on the plenum. Insert a T-pipe there (pic
. Attach a pressure gauge to the T and tighten
l clamps.
ow reconnect the fuel pump harness and
essurize the system by turning the ignition
y 3 times ON and OFF (the fuel pump
perates for a second or two after ignition on,ou should be able to hear it).
heck for leaks and start the engine.
he fuel pressure at idle should be
proximately 2.5bar (36 psi)
he fuel pressure should rise with the pressure
the intake manifold.
isconnect the vacuum line from the pressure
gulator (pic 9) and the fuel pressure should
se to ~3 bar (~43.4 psi)
CV-valves:
he Positive Crankcase Ventilation valves are
cated under the plenum on its right and left
de (see pic 10)
aulty PCVs can cause crank case air to be
cked in to the plenum at times when it's not
pposed to.
hey can also get stuck closed so thatcessive pressure is built-up inside the crank
se causing the engine oil to leak
rough the rear main seal and sometimes the
l dipstick to pop out.
here is also one more symptom that happened
me. The spring inside the PCVs got weak so
ey opened wile braking and
at caused the engine to stall after a fairly hard
aking.would recommend everyone with an older Z
replace them. They cost~$3.4 so it's not a
g deal (PN 11810-40P00).
e sure to get new rubber hoses since the old
nes are probably hard as a rock and you have
cut them.
he part numbers are 11826-30P11 for the left
ne and 11826-30P01 for the right one (~$23
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tal).
emove the battery while replacing the PCV
n passenger side.
o not over torque them when installing, you
n brake the plenum!!
ompression test:
lways a good way to see the condition of thegine internals, especially if you find that
ere is a problem with a
rticular cylinder when looking at its spark
ug.
elow is the procedure as described in the
ervice Manual (except for the fusible link).
1. Warm up the engine
2. Turn ignition switch off 3. Disconnect the fusible link (by the
battery) named "Fuel pump, Inj."
4. Remove all spark plugs
5. Attach compression tester to no. 1
cylinder
6. Depress accelerator pedal fully to keep
the throttle bodies wide open.
7. Crank engine and record the highest
gauge indication8. Repeat the measurement for each
cylinder.
lways use a fully charged battery to obtain
e specified engine revolution (~300RPM)
hile cranking.
ompression pressure:
q Standard: 12,85 bar (186 psi) for NA ;11,79 bar (171 psi) for TT
q Minimum: 9,81 bar (142 psi) for NA ;
8,83 bar (128 psi) for TT
q Maximum difference between
cylinders: 0,98 bar (14 psi)
cylinder pressure in one or more cylinders is
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w, pour a small amount of engine oil into it
rough the spark plug hole and retest
mpression.
q If adding oil helps compression, piston
rings may be worn or damaged. Replace
piston rings after checking the piston
for damage.q If pressure stays low, a valve may be
sticking or seating improperly. Inspect
and repair the valves and their seats.
q If compression in any two adjacent
cylinders is low and if adding oil does
not help, there may be a leakage past
head gasket surface.
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