Chronic low idle, Toyota Drive-by-wire system

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I am trying to fix a chronic low idle problem in a 2002 Lexus ES300. This is the 4th gen. ES (2002-2006 300/330), with the 1st generation Toyota drive-by-wire system. The low idle has been persistent for years and resisted most common diagnostic methods or simple maintenance. The car drives superbly and has no error codes. Other owners report the same on the make forums, but there's no common-wisdom fix. On a 3ES or earlier Toyota, the main culprit is a dirty Idle Air Control Valve, though usually accompanied with rough warm idle. These DBW models do not have that IACV under the throttle body.

Over the years I have maintained the car well, with much more than "by the book" maintenance. I have had the valve covers off for new seals, new intake gasket, new platinum plugs. The intake systems has been reviewed a number of times for leaks with no luck, most recently a month ago. I go over all the vacuum hoses once a year at least and replace anything suspect, and did that last fall most recently. The car regularly idles when warm at 600rpm, verified with Torque/OBDII system and not just the cluster gauge. In the past, I could sit at a stoplight and slip the car into neutral, and the idle would rise a bit to 675/700. No longer; it stays at 600 now regardless when it's warm, a/c or no load. While the idle is low, it is consistent and not rough, and the car runs absolutely perfectly otherwise, so it defies common symptoms.

Last week I removed the intake and also broke the throttle body into it's two parts. There is an upstream section with a single venturi and a heater warming circuit plumbed through it. I've cleaned that often and it was very clean. I scrubbed it thoroughly with a bottle brush soaked in B12 anyway. In the 2nd section (behind the metal intake screen), there are two venturis and a butterfly valve on one of them, I did the same thing. I have never done this area before, It was fairly clean, but what the hey. I also pulled out the MAF sensor from the resonator box intake section, which was very clean upstream but a little dirty on the downstream side. I cleaned it gently with dilute dish soap and water on a q-tip; I had last cleaned it maybe three years ago. The car now idles around 650/675. Which is a small and helpful improvement, but one I suspect is going to degrade again over the winter. Unfortunately, I did multiple things at once (cleaning the twin-venturi section which I had never done before, and also cleaning the MAF sensor a little bit, which has been done in the past), so I can't nail down what made the change.

I suspect I need to think about the solenoid that powers the throttle plate? Is there a way to check the voltage going to it with the car running? What else do I need to look at and how to test it? I don't intimately know this DBW system works other than reviewing some youtube videos/online diagrams, and haven't been able to find diagnostic procedures. It is probably something simple, but at this point people just recommend throwing parts at the problem (which gets pricey fast, and is something that just offends my mechanical/diagnostic sensibilities).

Does anyone have a lot of familiarity with this Toyota system and has seen older ones/high mileage ones act up like this?
 
Wonky Crank sensors can cause this as well. If you have a good quality scan tool you can set it to do an idle Re-Learn.
 
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Originally Posted by StevieC
Wonky Crank sensors can cause this as well. If you have a good quality scan tool you can set it to do an idle Re-Learn.


The generic re-learn proceedure (ecu rest) result in the same idle. Is this something different?

The vibration at the low idle is annoying, and unwanted on a car with inadequate engine mounting. This is a known problem on these. I have corrected worn mounts and struts on the car and want to avoid future wear, as well as the vibration, however subtle, at idle. At any idle above 700 or 750 or so, the car is very smooth.
 
It might have a generic and another more advanced that professional scan tools can trigger. I'm not sure if about your specific vehicle. I know in Chrysler there is 2. One that anyone can do when the Throttle Plate is cleaned for example and another one our scan tool ($10K) can do that involves calibrating the pedal and the electronic plate both with the engine running and shut down.

I would check into the crank sensor. If it's not fully pulling the signal to ground or has some noise this would affect the idle because the ECM doesn't know the true value.
 
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Also....


Pedal Relearn Procedure
Accerlerator Pedal Released Postion Learning is and operation to learn the full released postions of the accerlerator pedal by monitoring the accelerator pedal sensor output signal. It must be performed each time harness connector of accelearator pedal postion sensor or ECM is disconnected.

1. Make Sure the acceleartor Pedal is fully released
2. Turn Ignition switch ON and wait at least 2 Seconds.
3. Turn ignition switch OFF and wait at least 10 Seconds
4. Turn Ignition switch ON and wait at least 2 seconds.
5. Turn Ignition switch off and wait at least 10 seconds

Throttle Valve Relearn
Throttle Valve Closed Postion Learning is to learn the fully closed postion of the throttle valve by monitoring the throttle position sensor output signal. It must be performed each time harness of
electric throttle control actuator or ECM is disconnect.

1.Make sure accelerator pedal is fully released.
2. Turn ignition ON
3. Turn igntion switch OFF and wait at least 10 seconds. Make sure that the throttle valve moves during the 10 seconds by confrming the operating sound.
(You can hear the TB sound when you have key on and shifter in first gear and step on the gas. So you know what you listening for.)


Idle Air Volume Relearn Procedure
The Following Condtions Must be met in order for procedure to Work.

Battery Voltage :More than 12.9 volts at idle
Engine Coolant Temp 158-203 degrees Farenhiet
Electric Load Switch OFF i.e Air Condition, headlamps , rear defogger
Steering Wheel: Neutral Postion (Straight Ahead)
PNP Switch: OFF (Park Neutral Switch i.e. Clutch Switch...pretty sure)


1. Perform ACCERLEARATOR PEDAL RELEASED POSTIONS LEARNING
2. Perform THROTTLE VALVE CLOSED POSITION LEARNING
3. Start engine and warm it up to operation temperature
4. Turn igniton switch OFF and wait at least 10 seconds
5. Confirm Gas Pedal if fully realeased, then turn igniton switch ON and wait 3 seconds
6. Fully step on and release gas pedal 5 time within 5 seconds
8. Wait 7 seconds and fully step on gas and stay on until MIL stops blinking and is steady.
9. Fully release the Gas pedal within 3 seconds after the MIL has turned ON steady.
10. Start engine imediatly and let idle. Wait 20 seconds.
 
Great. I will tackle that this weekend, and check he cps angle you mentioned, also. Thank you very much.
 
Good luck
thumbsup2.gif
 
Was just messing with my v6 Camry ps pump and found a pressure switch and wire that presumably boost the idle when steering. Might want to watch your live data to see if you have this and it's working how you expect. May not throw a code either as it's a comfort thing not emissions.
 
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Originally Posted by eljefino
Was just messing with my v6 Camry ps pump and found a pressure switch and wire that presumably boost the idle when steering. Might want to watch your live data to see if you have this and it's working how you expect. May not throw a code either as it's a comfort thing not emissions.


Good point, I am aware of that boost circuit. I know mine is working as I redid the PS pump two or three years ago and I tested it then, and this has been independent of that. However, thanks for pointing that out and it may benefit other people.
 
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