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Victor
Victor, Toyota Master Technician
Category: Toyota
Satisfied Customers: 759
Experience:  Toyota Master ASE Certified, Prius/ Highlander/ Camry Hybrid Certified, trained in all areas
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2001 Toyota Corolla: 2000 rpm..slowly..this cold idle speed..OBD

Resolved Question:

Hi, I Have a 2001 Toyota Corolla IAC valve question. When I start the car cold on a 70 deg day it winds up to 2000 rpm for about 30 seconds and slowly works down to 800 rpm. Does this sound right and can I adjust this cold idle speed with my OBD 2 PC tuner software?
Submitted: 2 years ago.
Category: Toyota
Expert:  Victor replied 2 years ago.
Thanks for using JustAnswer.

As the temperature decreases, the cold start up will compensate by raising the idle to warm up the engine at a quicker rate. This feature is programmed into the engine's ecu and unfortunately it is not adjustable.
Customer: replied 2 years ago.
Hi Victor, thanks for getting back. The real problem I'm having is this engine winding up to 2000 rpm on a relatively warm day. It seems like 2K rpm from a dead cold start is a bit much. Oil hasn't gotten to the valves yet. You say there is no way to adjust this via the ECU. I was hoping there was. Do you have the resources to provide documentation with an illustration of the internal connections of the IAC motor for this vehicle? I'm also wondering how this IAC motor is controlled by the ECU. I was reading about the way the different types of motors were controlled. Some with pulses and some with DC voltage. I am currently monitoring the DC voltage on the three pins of the motor. The center seems to be the common. As the engine warms up and idle changes, the voltage from the the center to each pin changes accordingly.
I don't know if this is something you can give me help with. If you can get me this information I will make it worth your while. Looking forward to your response. I'll be here to accept pretty much as soon as you respond.
Thanks,
Customer
Expert:  Victor replied 2 years ago.
I do not have access to the information that you've requested, but the engine's ECU does monitor the engine's coolant temperature to control the IAC motor. Depending on the temp. the ECU will either increase or decrease voltage to the IAC. The center wire is the control wire and the other two wires are power and ground. From the description you provided, it sounds like it is working. 2000 RPM's does sound a little high on a warm day. From experience, I have not seen too many bad/shorted IAC motors on the 1ZZ-FE engine's. But, what I have seen is carbon build up inside the IAC valve. If there's too much carbon on the valve, it will intermittently stick and cause erratic idle. Have you tried removing the
IAC and cleaning out the valve with carb cleaner?
Customer: replied 2 years ago.
No I haven't removed it yet because it appears to work smoothly although the 2k initial idle starting point is high and I can't help being concerned. That's interesting you say the center is control and the others are power and ground. Do you know if this is truly a motor or a solenoid of some type that moves a valve depending on the voltage applied. Also do you agree it is a DC voltage that changes valve position. That is how it was on my 1991 Celica.
And yes, this is a 1ZZ-FE engine. My 1991 Celica was a 5S-FE. That was OBD 1 of course. This being OBD 2 makes me wonder if they changed the actual way the IAC motor is controlled. Do you think this IAC can be operated by applying the correct power and ground connections and then varying the control voltage? I'm kind of determined to manually control this motor. Removing the connection to the IAC gives me a check engine light condition. Is there a way to fool the ECU by simulating the presence of an IAC motor on the connector?
When I remove the connector even though I get a check engine light the idle is nice and low when it starts cold. I know this isn't the answer. Have you seen these engines idle at 2K for over 30 seconds before they slowly come down? And doesn't that harm the engine? What is the idle speed usually on these 1ZZ-fe on a cold start? Any other helpful information would be so appreciated. As you can see this is more of a project than a repair and I'd like to accomplish it.
Thanks again Victor, if you have no other suggestions I'll just accept. I hope you do...
Expert:  Victor replied 2 years ago.
The IAC is a stepper motor and is controlled via 5 volt reference. I'll be honest, I've never been asked to manually control the IAC motor just because the potential of frying the ecu if not done perfectly. You could POSSIBLY wire in a variable resistor, like a potentiometer, inline the common wire to control the amount of voltage going to the IAC, but I've never seen it done nor tried it myself. By doing this, it should not trip the check engine light because you are not creating an open or short circuit. Just a thought. When you unpIug the IAC, the ecu will go into fail safe mode a idle the engine to predetermined speed, also programmed into the ECU. I do notice that these engine's do rev high when cold, as high as 2500 RPM's. Do I think it's safe for the engine, well it depends on how strong the oil pump is on initial startup. If the oil pump is good, it will prime the cold engine in a matter of 2 seconds. If the oil has been religiously changed every 3k miles, you shouldn't worry about a weak oil pump. Hope this clears things up a bit for you.
Victor, Toyota Master Technician
Category: Toyota
Satisfied Customers: 759
Experience: Toyota Master ASE Certified, Prius/ Highlander/ Camry Hybrid Certified, trained in all areas
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