I have ordered a new IAC for my 97 LC with 290k miles. The existing IAC failed the test listed in the FSM; idle speed is sometimes poorly controlled. Will the computer have to learn the new IAC?
IAC Replacement (1 Viewer)
- Thread starter richw99
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I just replaced mine. It immediately idled better. Went from a random stutter to smooth
Malleus
Far west of Siegen
No. The IAC is a valve. It opens and closes according to the input it gets, based on the engine coolant temperature.
FWIW, the 80 series ECM isn't a learning computer. All of the control values are preset.
- Thread starter
- #4
Thanks ZRTacticall and Malleus. When the engine is turned off, does the valve always go to full open or does it open gradually as ect goes down?
After turned off the engine, it will be completely open inside, even hot engine, after starting it is regulating instantly , do you suffer from you do not have high idle on a cold engine?
If so, did you remove throttle body? Did you replace d the gasket? New Thrtl and iac gaskets is very important for a stable idle.
Malleus
Far west of Siegen
The valve plunger is controlled by the stepper motor. It stays wherever the motor last stopped. This is why the FSM validation procedure mandates that you completely cycle (all four steps) the motor when testing.
The only way the valve would move whether the engine is hot or cold, is if the motor received a signal to move.
While the IAC valve is out is a good time to completely clean the Throttle Body, all ports and passageways. 99% of the time when someone "cleans" the TB they just spray solvent into/onto the butterfly plate but IME there's a lot more that needs cleaning especially with high miles.
The best way to do that IME is to remove it from the engine. I mark the cables (nuts-threads) before removing them with a dab of paint to make it easier to get them back to where they were. Good time to check cable adjustment also.
You'll need some OEM 3.5mm vacuum hose and ~5" section of the fuel rated hose to replace the fatter hose that runs from the top of the TB to a small pipe.
There is a bit of a trap in doing this; with the TB removed you can then see how nasty the intake plenum is so you'll have the urge to clean that also, and the best way to clean that is to take at least the top half off. IME you can clean a lot of the gunk and sludge and carbon off from inside the upper plenum while working on it in place, but you can end up spending more time leaning into the engine bay doing it that way.
And then with the TB out of the way it's a perfect time to replace the Valve cover gasket along with the spark plug tube seals and valve cover grommet if those jobs havn't been done in awhile.
And with the cables disconnected from the TB is a good time to repair/cover any peeling rubber covering the cables using something like 3M dual wall adhesive lined flexible heat shrink tubing. It's available in various diameters, shrink ratios, and lengths including 2' and 4'.
And with that out of the way is a good time to replace the heat control valve if it's old/orginal.
And while you're in there you can add heat (insulation) wrap to the main engine harness near the EGR pipe and then remove and clean the EGR valve, replace all vacuum hoses, etc,etc,etc..
One job can turn into 18.
FWIW
The best way to do that IME is to remove it from the engine. I mark the cables (nuts-threads) before removing them with a dab of paint to make it easier to get them back to where they were. Good time to check cable adjustment also.
You'll need some OEM 3.5mm vacuum hose and ~5" section of the fuel rated hose to replace the fatter hose that runs from the top of the TB to a small pipe.
There is a bit of a trap in doing this; with the TB removed you can then see how nasty the intake plenum is so you'll have the urge to clean that also, and the best way to clean that is to take at least the top half off. IME you can clean a lot of the gunk and sludge and carbon off from inside the upper plenum while working on it in place, but you can end up spending more time leaning into the engine bay doing it that way.
And then with the TB out of the way it's a perfect time to replace the Valve cover gasket along with the spark plug tube seals and valve cover grommet if those jobs havn't been done in awhile.
And with the cables disconnected from the TB is a good time to repair/cover any peeling rubber covering the cables using something like 3M dual wall adhesive lined flexible heat shrink tubing. It's available in various diameters, shrink ratios, and lengths including 2' and 4'.
And with that out of the way is a good time to replace the heat control valve if it's old/orginal.
And while you're in there you can add heat (insulation) wrap to the main engine harness near the EGR pipe and then remove and clean the EGR valve, replace all vacuum hoses, etc,etc,etc..
One job can turn into 18.
FWIW
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Malleus
Far west of Siegen
What he said...
mudgudgeon
Resident galah
Malleus
Far west of Siegen
You make me laugh. LMK when you get to Asheville. We need to drink a few.
mudgudgeon
Resident galah
- Thread starter
- #13
Thank you for reply. Sometimes, hot or cold I have high or low idle. It always slowly adjusts back to 600-650 rpm. The LC has been in my family since new; if the throttle body was ever off, it was a long time ago. I will see what new iac wiil do when it arrives; hopefull they will include a new O ring. Thanks again
Good chance to clean it too
IIRC the O-ring (90079-60004) does not come with an OEM IAC (22270-66011), you have to order that separately. IME sometimes
aftermarket part come with the gasket or O-ring when Toyota you have to order it as a separate part.
Example: a Toyota water pump comes just with the water pump but the studs for the pulley and fan are already installed. The identical AISIN aftermarket waterpump comes with the studs unattached in the box along with the metal gasket.
FWIW
aftermarket part come with the gasket or O-ring when Toyota you have to order it as a separate part.
Example: a Toyota water pump comes just with the water pump but the studs for the pulley and fan are already installed. The identical AISIN aftermarket waterpump comes with the studs unattached in the box along with the metal gasket.
FWIW
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