High idle, probably broken IAC, questions

[fixkick]

Update: 1991 Vitara MT, 2 door, G16a, 4wd.

Very shortly after experimenting with golf tee I moved the hose on driver's side near driver's right knee and put a moped's fuel valve at the end of the hose to be able to tune the vacuum leak and have RPM control.

cold 200-2200 (fully closed - fully open)
hot  800-2500 (fully closed - fully open)

Note a needle valve would be a lot better for selecting RPM as its designed for gasses, this valve is for liquid so the whole tuning range is around 2-3 degrees of rotation. Bit hard to tune, but it does what is needed.

wow, thanks for sharing all that data.  nobody has done this and posted the results. for building a fake,IAC valve, due to stock valve IAC stuck.(dead or weak)
that gas line valve is prefect. and easy to find too.

the dash gauge water temp uses its own 1 pin sensor and is not used for EFI , not used at all for the ECU for fuel mixing.

nice work and good luck for inspecting, get car hot, turn new valve for 800 rpm and bingo.
as you turn the valve , the ISC will kick in and do RPM controls HOT. to 800. (regulated ISC mode) hot.

i see yours did here. hot >>>> 800-2500 (fully closed - fully open)
 
the 2500 is because your  air leak is more than the ISC can control. 

try 1500 rpm cold see if when hot the ISC wakes up at 150F and goes to 800 like it should.


best wishes and cheers to you !


wow I missed your post before with super nice IAC packing job to take it off line..(leaking bad hot)  great photos those, and the method is perfect.
any method that can be Regressed easy  is best.  (blocking the base gasket also kills the air bleed in top of air horn, and is best to keep that working)

Thanks hope that someone having same problems can use this thread to sort out IAC problems
. Also my goal here was to try to achieve debug and possible fix for the IAC without removing the TB from the car.
I had tested everything else except IAC and checked the TB gaskets.


I have previously diagnosed by ISC being dead too or then impaired by something (bad TV position?).

It does absolutely nothing when I turn on head lights  (only on 89/90 USA) or high beams. 80/90 only
Hot idle up pin reacts to defroster, but ISC does not. (heater blower, = defroster???) or rear glass of car resistor heater defroster?

91 does only dash blower in heater, idle up, and PS overload, (and rear glass heater only if fitted and does AC idle up if factor AC is present and working.
All iDLE ups are hot idle only, and  only work if hot engine, not cold.
idle ups are all ECU to ISC modulation methods called PWM.
IDLE UP MODES. FAIL
IF , NOT HOT ENGINE, 180F (common)
ISC clogged in side or coil inside open 
idle up pins into the ECU dead. (sensors for that wrong)
the TPS idle pin stuck at 5vdc ( means TPS is bad or just not calibrated using the factory TPS calibration that ends with TPS idle pin at 0v. (dask pot disabled)
Dash put stuck extended. hot idle. well this must be cured.
TV valve set wrong . stop screw. wrong on 80/90 but on 91+_ USA, it is set closed. and has bleed air screw in the front top TB air horn..
If at any time the hot idle is not normal 800rpm (+-50) that means the ISC is dead or just  off line. if off line idle up fails too, (a dual failure that0
ISC will fail if IAC is bad, if any device in the engine allows air to suck in illegally (IAC too) the ISC will fail, or even HUNT. (wild Rpm changes as ECU hunts the ISC like mad for 800)

this OP post is 91, not 89/90 and in USA those are totally different ECU and idle controls, for sure Idle up not the same.

My hot idle is around 650 with lights and blower. (hot or cold? engine) ISC only works HOT.
600 with lights + high beams + blower + seat warmer. 800 when all lights and blower off.
Feels like someone has tuned it to 800 on that setup.

Vehicle passed inspection 3 weeks ago. I just forgot to update the valve pic here and remembered it due to the "1989 screamer" thread.

I do not care the hot idle not being modulated as it does not affect my driving at all. Oil pressure is ok enough (light off), battery is charged even on such low RPM and engine never stalls even if I step on clutch and lift throttle suddenly during driving.

Ie the only pain it causes is that it does not keep 800 RPM. But here for pre 92 or 93 cars the emission spec is pretty easy. Certain emission levels & RPM <= 1000.

Newer cars will be tested idle and high RPM and for diesels box on neutral a engine acceleration from idle to max RPM on full throttle to see how much smog an particles they do.

let me talk about ISC and command authority.HOT engine only ISC only functions hot. (cold is IAC)

this is also about idle duty cycle settings called (TPS calibration)  TPS set right gets the TPS idle switch pin to 0volts DC. (which enables hot  idle controls) 5v turns it off.

the ISC on a hot engine can only change idle speeds with in its range of authority,   (minus 300 to plus + 300 rpm)
this range varies by out door air temps , engine wear or its internal friction. (or its power week or normal)
but when you set duty cycle to 50% (tps cal does that ,using 91 air horn, bleed screw) we set 50%
this make the ISC be in the center of its range,(of authority)

any illegal air leak (vacuum) wrecks this 50% center point,

I have no photo of front of your TB,  ?
like my 91 here. (usa onlyk, in europe changes happen on different years) and also idle up rules not the same as our.

the purpose of this bleed screw is only 2: (1 actually it allows duty cycle setting 10x more easy than 1989/90 USA.
the 89/90 USA are a pain  the TV valve is set for duty cycle but this act can and will cause the TPS calibration to now fail and idle switch opens and kills dead the ISC.
the cure  for that is not simple but is this.
one makes sure the TPS switch stays closed,(idle switch) and adjust the 89./90 TV screw(hot) to get ISC voltages at 50% then last calibrate TPS.
in 91 this is vastly more easy ,we must set TPS first the duty cycle last at the bleed screw below.

in europe some cars (for sure  Santana from spain) has 90 year ECU in 97 year car. wow. tricky.

this is USA spec car 91 and is last 8v sold in USA< banned by EPA after. only 16v after 92 up.(G16)

91+ (engine must be hot, TPS idle pin at 0vdc a must)
no illegal vacuum leaks, (cracked hoses) 
IAC must not leak, after all it is closed fully after 150F and for sure at 180f real hot temp (thermostat not bad for sure not stuck open)

How to set duty cycle more easy?
use an old style (cheap) analog voltmeter, VOM, volt ohm meter. ( most of DMM fail here, do not use DMM unless have 10 kinds to try, no)
set DMM  to 12vdc scale or 15vdc,
put the test leads across the ISC 2 wires, (not easy we use back probing on 91)
TURN the bleed bleed  to meter to 7vdc or 1 half of alternator battery voltage , can be 13.3 volts  or 15 or 14.7.  

this ISC voltage is this. my old scope,
5volts DC is the vertical scale and 200 Hz square wave , it goes with out saying the scope does not lie, DMMs do on square waves
high is 15v ISC is open
0volts is ISC closed
so and analog meter (needle scale) will be 1/2 or 7.5vdc  it averages the voltage, and if wrong turn the bleed until needle lands on 7.5vdc (1/2 battery voltage hot,

the below is not a goal ever, it is not a real hot engine, running, Pulse width modulated. the real goal is 1/2 high and 1/2 low hot.
the ISC moves 200 times a second. in and out. the duty cycle of which sets RPM to 800. (or idle up speed) hot.



step one on all 8v is see of  the bleed screw is there?