high idle and low idle???
02-24-2009, 11:57 AM
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high idle at operating temp
when i get off a freeway, highway, or any high speed driving it seems to be. my idle is about 1500. and sometimes when i start my car after its warmed up it idles at about 800?? does anyone know what this could be? my FSM doesnt really cover this kind of problem? my guess is a iac or idle sensor?
Last edited by alexcarey; 03-16-2009 at 10:07 AM.
02-24-2009, 02:59 PM
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A high idle immediately after hard driving which settles to a low idle after a bit of idling can be caused by a faulting coolant temp switch (not likely but possible), a malfunction or misadjusted throttle position sensor (likely), vacuum leaks (likely), malfunctioning idle air valve \ auxillary air valve (possible with a higher mileage engine or one which the coolant isn't serviced regularly), improper ignition advance, failing O2 sensor....
The ECU on the pre-95 trucks and 4Runners is not capable of adjusting idle speed on its own. It relies on mechanical means: the idle air bypass screw on the throttle body, the idle air valve / auxillary air valve (name changes depending on year and application) and with air conditioning the a/c idle up vsv.
The idle air bypass valve does what it's name implies- allows air to bypass the throttle plate when the throttle is closed. It sets the base idle speed when the engine is warmed up.
The idle air valve / auxillary air valve is located under the throttle body and is heated by coolant. It's purpose is to raise the idle speed when cold and lower the idle speed as the engine warms up. If it is malfunctioning it can cause odd operation such as what seems to be a perfect idle when started which deteriorates into a poor idle when warmed up, inability to set the warm idle speed or a poor idle when cold which stabilizes when warmed up.
The A/C idle-up VSV is a 'vacuum switching valve (VSV)' that operates when the a/c is turned on. It does a similar thing to the idle air bypass screw in that when activated it allows air around the throttle plate in order to raise the idle speed and compensate for the drag on the engine from the a/c compressor.
Then we need to consider the Throttle Position Sensor (TPS). If it does not register the correct throttle position to the ECU, the ECU may try to inject an improper amount of fuel and / or may look at the O2 sensor when it should not be referenced, in particular when the throttle is closed or wide open. For example- if the TPS is not signalling the throttle is closed to the ECU, the ECU will be looking at the O2 sensor for feedback and since the engine is at idle there is not sufficient exhaust volume across the O2 sensor for reliable feed back and the ECU may think the mixture is too rich and consequently lean the mixture out causing the RPM's to rise until the O2 sensor cools off somewhat (sound familiar?). The coolant temp sensor can cause a similar 'mode' of operation as well.
Ignition timing is a culprit since cylinder head and coolant temps as well as combustion temps (and consequently exhaust temps) are very dependent on ignition advance (or retard).
If I had to theorize about your truck... first thing I would do is check for any trouble codes stored by the ECU and repair any of those issues. Next I would test the thermostat to ensure it's operating properly, replacing if necessary. Next- check for vacuum leaks, including exhaust leaks and repair any if found. Then I would check / adjust / replace the TPS as necessary and set the timing to factory specs. If that didn't clean it up, I would check the idle air valve / auxillary air valve to verify it is operating properly (cold idle speed should be 1000-1500 depending on initial ambient temperature, dropping to 800 with the engine fully warmed up). Following that, testing the coolant temp sensor to the ECU should be done. If I was still having a problem I'd do a compression check to make sure the cylinders are all operating properly.
Sorry I couldn't help more.
The ECU on the pre-95 trucks and 4Runners is not capable of adjusting idle speed on its own. It relies on mechanical means: the idle air bypass screw on the throttle body, the idle air valve / auxillary air valve (name changes depending on year and application) and with air conditioning the a/c idle up vsv.
The idle air bypass valve does what it's name implies- allows air to bypass the throttle plate when the throttle is closed. It sets the base idle speed when the engine is warmed up.
The idle air valve / auxillary air valve is located under the throttle body and is heated by coolant. It's purpose is to raise the idle speed when cold and lower the idle speed as the engine warms up. If it is malfunctioning it can cause odd operation such as what seems to be a perfect idle when started which deteriorates into a poor idle when warmed up, inability to set the warm idle speed or a poor idle when cold which stabilizes when warmed up.
The A/C idle-up VSV is a 'vacuum switching valve (VSV)' that operates when the a/c is turned on. It does a similar thing to the idle air bypass screw in that when activated it allows air around the throttle plate in order to raise the idle speed and compensate for the drag on the engine from the a/c compressor.
Then we need to consider the Throttle Position Sensor (TPS). If it does not register the correct throttle position to the ECU, the ECU may try to inject an improper amount of fuel and / or may look at the O2 sensor when it should not be referenced, in particular when the throttle is closed or wide open. For example- if the TPS is not signalling the throttle is closed to the ECU, the ECU will be looking at the O2 sensor for feedback and since the engine is at idle there is not sufficient exhaust volume across the O2 sensor for reliable feed back and the ECU may think the mixture is too rich and consequently lean the mixture out causing the RPM's to rise until the O2 sensor cools off somewhat (sound familiar?). The coolant temp sensor can cause a similar 'mode' of operation as well.
Ignition timing is a culprit since cylinder head and coolant temps as well as combustion temps (and consequently exhaust temps) are very dependent on ignition advance (or retard).
If I had to theorize about your truck... first thing I would do is check for any trouble codes stored by the ECU and repair any of those issues. Next I would test the thermostat to ensure it's operating properly, replacing if necessary. Next- check for vacuum leaks, including exhaust leaks and repair any if found. Then I would check / adjust / replace the TPS as necessary and set the timing to factory specs. If that didn't clean it up, I would check the idle air valve / auxillary air valve to verify it is operating properly (cold idle speed should be 1000-1500 depending on initial ambient temperature, dropping to 800 with the engine fully warmed up). Following that, testing the coolant temp sensor to the ECU should be done. If I was still having a problem I'd do a compression check to make sure the cylinders are all operating properly.
Sorry I couldn't help more.
Last edited by abecedarian; 02-24-2009 at 03:00 PM.
02-24-2009, 03:09 PM
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thank you. i will look into this. sorry for being inpatient but truck problems and trying to get input is like pulling teeth. well, weve all been there right?
02-24-2009, 03:14 PM
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i just replaced my o2 sensor and it was happening before i replaced it as well. and could the vsv be related even if i dont have the ac turned on? from what you described it sound that the coolant temp switch could be the problem. because it will eventually lower in rpm but will not with a pump of the gas pedel. do you know the specified ohm resistance on the coolant temp sensor?
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02-24-2009, 03:21 PM
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True, we've all been there at one point in time (or maybe several 
).
Just realize that not everyone that looks at the forums looks at every thread. Many use the Forum's "Search" for what they think may be keywords to help them figure their problem out. As well, others don't look at threads which have replies because they may think the situation is being resolved by someone else so it may take a while or others to view the thread and weigh in with their opinions.
). Just realize that not everyone that looks at the forums looks at every thread. Many use the Forum's "Search" for what they think may be keywords to help them figure their problem out. As well, others don't look at threads which have replies because they may think the situation is being resolved by someone else so it may take a while or others to view the thread and weigh in with their opinions.
02-24-2009, 03:23 PM
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If you're not experiencing detonation when the engine's hot and have ruled out the other things associated with the idle, I'll get you the test specs on the temp sensor... because I don't think that's your problem.
02-24-2009, 05:29 PM
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If anyone figures this out I would appreciate a heads up because I am having the same trouble. Here is my history, the idle got really high, about 2200 when cold, dropping to about 1600 when warm. The next day, my truck over heated somewhat, I checked the thermostat. Turns out that I had the dreaded timing chain through the cover problem. Water in oil and oil in water. I have just fixed the chain and cover, and the intake manifold as I broke the damn bolt holding the thermostat housing. Sounds like the fast idle, in my case at least, is related to the coolant issue. What do you gracious, knowledgeable, folks think?
02-24-2009, 05:33 PM
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May I suggest starting your own thread for this problem?
If anyone figures this out I would appreciate a heads up because I am having the same trouble. Here is my history, the idle got really high, about 2200 when cold, dropping to about 1600 when warm. The next day, my truck over heated somewhat, I checked the thermostat. Turns out that I had the dreaded timing chain through the cover problem. Water in oil and oil in water. I have just fixed the chain and cover, and the intake manifold as I broke the damn bolt holding the thermostat housing. Sounds like the fast idle, in my case at least, is related to the coolant issue. What do you gracious, knowledgeable, folks think?
03-01-2009, 10:01 AM
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sorry about that...
basically, between the two terminals on the sensor (color coded red is upper limit, blue is lower limit, green is preferred)
some more 411 here (page 6 of the PDF): www.autoshop101.com/forms/h32.pdf
basically, between the two terminals on the sensor (color coded red is upper limit, blue is lower limit, green is preferred)
some more 411 here (page 6 of the PDF): www.autoshop101.com/forms/h32.pdf
Last edited by abecedarian; 03-01-2009 at 10:02 AM.
03-02-2009, 03:01 PM
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Hey guys, I'm new on this forum - but no stranger to the 3VZE. I've got a very similar problem with my 93' 3VZE powered 4Runner. I've cleaned up and attempted to adjust the idle air control valve (cranked it in some) to see if the problem would go away. Been chasing my own tail with the idle adjustment screw, and have verified the TPS is properly adjusted and has no flat/blank spots.
What it is currently doing is normal idle at cold start - 700-800, increasing to 1200-1300 once its warm. If I park the car for approx. 30 minutes then jump back in to take off, the idle is extremely low, and sometimes dies unless i keep my foot on the throttle. I also notice that it runs a bit rough through idle to 3k RPM, and smells very rich during this time.
If I leave it alone till its cooled completely, I'm back to 700-800 rpm. The O2 sensor hasn't been changed in a good 130K miles (238k current total), and I'm still on the factory ECT sensor. Is there any information on what pins to check at the ECM for the ECT. Even though my TPS checks out, it seems like the ECM is referencing the O2 at idle. My next step is to verify the ECT, and also adjust the Idle Air Bypass back to the factory location. I would hate to through parts at it, but I think a new O2 would be in order.
Any input on this would be appreciated!
P.S. I've serviced the coolant and verified the passages to the TB are good. Also pulled the idle fuel injector harness from the injector and nothing changes. I've only checked that at cool / warm idle when it seems to idle decently.
What it is currently doing is normal idle at cold start - 700-800, increasing to 1200-1300 once its warm. If I park the car for approx. 30 minutes then jump back in to take off, the idle is extremely low, and sometimes dies unless i keep my foot on the throttle. I also notice that it runs a bit rough through idle to 3k RPM, and smells very rich during this time.
If I leave it alone till its cooled completely, I'm back to 700-800 rpm. The O2 sensor hasn't been changed in a good 130K miles (238k current total), and I'm still on the factory ECT sensor. Is there any information on what pins to check at the ECM for the ECT. Even though my TPS checks out, it seems like the ECM is referencing the O2 at idle. My next step is to verify the ECT, and also adjust the Idle Air Bypass back to the factory location. I would hate to through parts at it, but I think a new O2 would be in order.
Any input on this would be appreciated!
P.S. I've serviced the coolant and verified the passages to the TB are good. Also pulled the idle fuel injector harness from the injector and nothing changes. I've only checked that at cool / warm idle when it seems to idle decently.
03-02-2009, 06:05 PM
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My o2 has about 1000 miles on it so it's probably not that. Check the resistance with an ohm meter and you can tell if it's bad if you want the work flow for that let me know
03-02-2009, 08:45 PM
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If you have info on checking/verifying the O2 that would be great. I've already gone through the TPS, and I see the chart from abecedarian for the ECT sensor.
I was just curious about the ECT being checked at the ECM rather than pulling the ECT and checking in a pot of water, or trying to access it installed on the car
I was just curious about the ECT being checked at the ECM rather than pulling the ECT and checking in a pot of water, or trying to access it installed on the car
03-16-2009, 10:05 AM
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update: so i checked my idle screw and what i noticed is when i have been driving it idles about 1500 but if i turn it off and back on it idles at 800. now if i give it any gas at all it jumps right back up to 1500 and will not drop back down unless i turn the car off and then back on. so its not my idle screw. i cant check the cool temp sensor because i could never get it to the right temprature to match the chart above. does anyone know what this might be?
03-18-2009, 06:37 PM
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An alternative way to check the ECT sensor is to backprobe the THW and E2 wires where they connect to the ecu. When the motor is hot and ignition is on, they should read 0.2 - 1.0 volts. See the MFI SYSTEM - TROUBLESHOOTING section of the manual.
On the tps, pay particular attention to the IDL-E2 terminals - that's your idle signal, and when throttle is closed (idle position), IDL to E2 should have continuity (less than 2.3k ohms). They should NOT have continuity (infinite ohms) when throttle is cracked open .77 mm or more. The other thing to check with tps is that resistance between VTA and E2 increases smoothly with no spikes or dropouts as the throttle is slowly opened. The tps specs in the 93 manual appear to have typos for the upper limit of the allowable range for VTA-E2 at the throttle closed position. 6.1k is probably wrong for a 93 motor - it's probably supposed to read .61k. Anyway, for the older motors, it's definitely wrong - my 89 manual shows 0.8k.
While you've poking around with an ohmmeter, may as well check your vaf meter, too. On that one, resistance between VS & E2 should change smoothly "in a wave pattern" with no spikes or dropouts as the vane is slowly pushed open.
The vafm isn't too likely to be causing your idle issues (still worth checking, tho), but a more likely possibility is the distributor. Check the signal rotor clearances and signal generating coil resistances (or just try a known good distrib). The signal rotors/coils generate crankshaft and camshaft position signals which are fed to the ecu and used by the ecu to set the spark advance. I had a longstanding pinging problem on my 3vze that defied years worth of efforts to find the cause. Two years ago I replaced the distributor because of shot bearings, and much to my surprise and delight, the pinging problem disappeared entirely. I believe faulty crank or cam position signals were causing the ecu to advance spark timing too much.
Specs and instructions for testing are in the fsm in the IGNITION - ON VEHICLE INSPECTION section.
You could get a used distributor, but unless it has less than say 100k miles, I'd worry it might have the same problem. My pinging problem started around 120-130k miles.
On the tps, pay particular attention to the IDL-E2 terminals - that's your idle signal, and when throttle is closed (idle position), IDL to E2 should have continuity (less than 2.3k ohms). They should NOT have continuity (infinite ohms) when throttle is cracked open .77 mm or more. The other thing to check with tps is that resistance between VTA and E2 increases smoothly with no spikes or dropouts as the throttle is slowly opened. The tps specs in the 93 manual appear to have typos for the upper limit of the allowable range for VTA-E2 at the throttle closed position. 6.1k is probably wrong for a 93 motor - it's probably supposed to read .61k. Anyway, for the older motors, it's definitely wrong - my 89 manual shows 0.8k.
While you've poking around with an ohmmeter, may as well check your vaf meter, too. On that one, resistance between VS & E2 should change smoothly "in a wave pattern" with no spikes or dropouts as the vane is slowly pushed open.
The vafm isn't too likely to be causing your idle issues (still worth checking, tho), but a more likely possibility is the distributor. Check the signal rotor clearances and signal generating coil resistances (or just try a known good distrib). The signal rotors/coils generate crankshaft and camshaft position signals which are fed to the ecu and used by the ecu to set the spark advance. I had a longstanding pinging problem on my 3vze that defied years worth of efforts to find the cause. Two years ago I replaced the distributor because of shot bearings, and much to my surprise and delight, the pinging problem disappeared entirely. I believe faulty crank or cam position signals were causing the ecu to advance spark timing too much.
Specs and instructions for testing are in the fsm in the IGNITION - ON VEHICLE INSPECTION section.
You could get a used distributor, but unless it has less than say 100k miles, I'd worry it might have the same problem. My pinging problem started around 120-130k miles.
