Car is a 97 Toy Avalon. The car has been idling high on and off for the past few months (~1500 rpm) even when fully warmed up (the car has a high idle built in, til the coolant is up to temp, it also short shifts during that cycle as well). For the past 2 days it has been idling high continuously and short shifting even with the pedal to the floor (it usually shifts at redline) the temp gauge is squarely in the middle as it should be, but it feels like the car thinks it is cold and is idling high and short shifting. My Q is, is there a way to tell what this is coming from AND if the computer thinks the car is cold, does the coolant temp sensor tie into the coolant temp gauge on the dash (ie, if the coolant temp sensor reads cold, the dash gauge will too)? Check Engine Light is NOT illuminated...THANKS FOR YOUR HELP!
Car Idles High and Short Shifts
- Thread starter parimento1
- Start date
- Status
Possible bad ECT. This sensor is different than the one for the temp guage (which is basically a dummy guage.)
JTK
$100 Site Donor 2025
Possible dirty/stuck idle air control valve? I'd pull it, clean it and it's port.
Joel
Joel
Yeah. Often there are 2 separate sensors - one each for the gauge and computer.
The IAT [air inlet temperature] sensoror TPS maybe faulty, also.
A vacuum leak or intake leak should be thoroughly checked out.
Each line and connection, the PCV system, and the intake.
Also, I'd clean the Throttle body bore and plate out real clean, and the idle air control motor. Use care with the IAC motor.
This should fix it, but if not, you did a wonderful maintenance thing and it will run that much better.
The IAT [air inlet temperature] sensoror TPS maybe faulty, also.
A vacuum leak or intake leak should be thoroughly checked out.
Each line and connection, the PCV system, and the intake.
Also, I'd clean the Throttle body bore and plate out real clean, and the idle air control motor. Use care with the IAC motor.
This should fix it, but if not, you did a wonderful maintenance thing and it will run that much better.
mechtech, if any of these are out of range, would it light the CEL. By the way, this morning the car ran fine...weird! However I will go over all those things tonight. If it was a vacuum leak would the problem be constant, or could it be intermittent?
vaccum leaks can occur at different temps. since metal expands when heated. Could possibly be a manifold gasket issue. If you have access to a vacuum guage and a scan tool that would be the best way to check everything. Typical vacuum on most modern cars is between 17-21hg. The ECT may not be the same unit that sends info the the cluster. Many cars use one sensor for the PCM/ECM and another for the cluster display. Also these temp sensors have specific ranges that they can operate within before setting a DTC. If a sensor is at the limit the PCM/ECM may think that everything is ok but in reality its not.
Watch that gauge carefully in traffic, if the ECT is reading cold you won't get the electric fan. (unless you run AC). Also your gas mileage will be worse.
Most OBDII cars complain when they can't reach their target idle RPM eg from a vacuum leak. However, if they want that high idle...
Most OBDII cars complain when they can't reach their target idle RPM eg from a vacuum leak. However, if they want that high idle...
Yea I would think a vacuum leak would cause a rough/low idle or stalling, not a high idle.
Originally Posted By: parimento1
Yea I would think a vacuum leak would cause a rough/low idle or stalling, not a high idle.
depends on whether or not its fuel injected and how big the vacuum leak is.
On fuel injected,most of the time the PCM can increase the injector pulse width to account for the additional air, essentially raising the idle in the process because of both the extra air and fuel. TBI's were noted for that because the base gaskets would eventually develop leaks and the engine would idle around 2,000 rpms.
Yea I would think a vacuum leak would cause a rough/low idle or stalling, not a high idle.
depends on whether or not its fuel injected and how big the vacuum leak is.
On fuel injected,most of the time the PCM can increase the injector pulse width to account for the additional air, essentially raising the idle in the process because of both the extra air and fuel. TBI's were noted for that because the base gaskets would eventually develop leaks and the engine would idle around 2,000 rpms.
Originally Posted By: parimento1
Car is a 97 Toy Avalon. The car has been idling high on and off for the past few months (~1500 rpm) even when fully warmed up (the car has a high idle built in, til the coolant is up to temp, it also short shifts during that cycle as well). For the past 2 days it has been idling high continuously and short shifting even with the pedal to the floor (it usually shifts at redline) the temp gauge is squarely in the middle as it should be, but it feels like the car thinks it is cold and is idling high and short shifting. My Q is, is there a way to tell what this is coming from AND if the computer thinks the car is cold, does the coolant temp sensor tie into the coolant temp gauge on the dash (ie, if the coolant temp sensor reads cold, the dash gauge will too)? Check Engine Light is NOT illuminated...THANKS FOR YOUR HELP!
You'll need to find out of the coolant temp sensor for the computer is also used for the dash. Some vehicles used two different ones, where newer models shared the same one for both purposes. This was a common problem on older S series Saturns. The older ones used one sending unit for the gauge and one sensor for the computer. A common problem with the S was the coolant sensor had a plastic tip and eventually they stopped working correctly. The engine would run really rich and the cooling fan would never come on because the computer never saw hot coolant temps even though the temp gauge was pegged at hot.
Car is a 97 Toy Avalon. The car has been idling high on and off for the past few months (~1500 rpm) even when fully warmed up (the car has a high idle built in, til the coolant is up to temp, it also short shifts during that cycle as well). For the past 2 days it has been idling high continuously and short shifting even with the pedal to the floor (it usually shifts at redline) the temp gauge is squarely in the middle as it should be, but it feels like the car thinks it is cold and is idling high and short shifting. My Q is, is there a way to tell what this is coming from AND if the computer thinks the car is cold, does the coolant temp sensor tie into the coolant temp gauge on the dash (ie, if the coolant temp sensor reads cold, the dash gauge will too)? Check Engine Light is NOT illuminated...THANKS FOR YOUR HELP!
You'll need to find out of the coolant temp sensor for the computer is also used for the dash. Some vehicles used two different ones, where newer models shared the same one for both purposes. This was a common problem on older S series Saturns. The older ones used one sending unit for the gauge and one sensor for the computer. A common problem with the S was the coolant sensor had a plastic tip and eventually they stopped working correctly. The engine would run really rich and the cooling fan would never come on because the computer never saw hot coolant temps even though the temp gauge was pegged at hot.
OK so I took the car out during my lunch break, same deal, high idling and short shifting, also shifts lazy when it does this. @FROGGY- good point, but would that account for the transmission short shifting? Also if I have a vacuum gauge where can I hook it up to to see if there is a leak, there are about 100000 different vacuum ports, like the brake booster, etc. The coolant temp sensor on my car is VERY easy to access, so all I need to know is the correct resistance for it and I am golden. I will try looking that up in the Toyota service manual I have at home.
Last edited:
depending on the size and location of the vacuum leak, you may not actually find it using a vacuum gauge, especially if the car is idling higher than normal.
Being that its a '97, hoses and plastic tubing like to dry rot and get brittle, could be very minute crack in a hose or line. I don't know much about Toyota and how they differ their shifting between hot and cold temps. If its like others, then it would most likely be tied to engine temps. I know the Intrepid I used to have would not go into overdrive on the highway until the temp gauge reached a certain point. Most of the time I would never know it because it would warm up fairly quickly in relation to getting on the highway. But in the dead of winter, it is most certainly noticable and how I found this out. Driving home in below 0*F weather from work one night and I couldn't figure out why OD wasn't locking in. Checked the service manual and saw that it was normal until the engine was warmed up enough. Yours may be similar.
Being that its a '97, hoses and plastic tubing like to dry rot and get brittle, could be very minute crack in a hose or line. I don't know much about Toyota and how they differ their shifting between hot and cold temps. If its like others, then it would most likely be tied to engine temps. I know the Intrepid I used to have would not go into overdrive on the highway until the temp gauge reached a certain point. Most of the time I would never know it because it would warm up fairly quickly in relation to getting on the highway. But in the dead of winter, it is most certainly noticable and how I found this out. Driving home in below 0*F weather from work one night and I couldn't figure out why OD wasn't locking in. Checked the service manual and saw that it was normal until the engine was warmed up enough. Yours may be similar.
According to Rockauto, they have listed in the parts both a coolant temperature sensor and a coolant sending unit. The sending unit could be for a gauge, otherwise if its just for a dash light it would only be a switch not sending unit. So since there are both a sensor and switch/sender, it is completely possible for the temperature gauge to read normally even if there is a problem with the sensor. GM and Ford have resistance vs. temperature charts out ther but I don't know if Toyota does. Something I would look into though if I were you.
The aforementioned sensor issue with the S saturns almost never showed by a lit check engine light.
The aforementioned sensor issue with the S saturns almost never showed by a lit check engine light.
one more thing. Usually a coolant temp sensor (CTS) shows higher than normal resistance, which leads the computer to read it as a very cold temperature. With that said, another symptom is higher than normal fuel consumption.
http://www.autoshop101.com/forms/h16.pdf
take a look at that. came across it looking for the temp vs. resistance for the temp sensor
take a look at that. came across it looking for the temp vs. resistance for the temp sensor
So on my ride home from work it was idling high and short shifting, about 1/2 way, about 30 mins into it, it started driving normally. I turned off the car when I got home, disconnected the coolant temp sensor, then started the car...the car ran fine- I was VERY surprised. Does this eliminate that as a source of the problem? I looked around the engine as well, I don't hear any hissing and all looks OK, most of the lines (as far as I could see) look good- no cracks or tears.
Originally Posted By: parimento1
So on my ride home from work it was idling high and short shifting, about 1/2 way, about 30 mins into it, it started driving normally. I turned off the car when I got home, disconnected the coolant temp sensor, then started the car...the car ran fine- I was VERY surprised. Does this eliminate that as a source of the problem? I looked around the engine as well, I don't hear any hissing and all looks OK, most of the lines (as far as I could see) look good- no cracks or tears.
was it the sensor or the sending unit for the gauge? if you unplugged it, did the check engine light come on?
So on my ride home from work it was idling high and short shifting, about 1/2 way, about 30 mins into it, it started driving normally. I turned off the car when I got home, disconnected the coolant temp sensor, then started the car...the car ran fine- I was VERY surprised. Does this eliminate that as a source of the problem? I looked around the engine as well, I don't hear any hissing and all looks OK, most of the lines (as far as I could see) look good- no cracks or tears.
was it the sensor or the sending unit for the gauge? if you unplugged it, did the check engine light come on?
It was the sensor the gauge still worked when it was unplugged and the CEL DID NOT come on...weird
Does that Avalon have a throttle valve cable from the throttle body to the transmission? Hard to believe, but my friend's 99 Camry i4 does, but that is a different transmission. My i30 does not, and it was made in 1996.
If there is no TV cable then the transmission control must rely on the TPS for throttle position input, so one guess is that it is getting an incorrect reading of the throttle position and thus shifting early and softly.
Can you test the throttle position sensor? I imagine they can get erratic. Just guessing here.
If there is no TV cable then the transmission control must rely on the TPS for throttle position input, so one guess is that it is getting an incorrect reading of the throttle position and thus shifting early and softly.
Can you test the throttle position sensor? I imagine they can get erratic. Just guessing here.
Originally Posted By: parimento1
It was the sensor the gauge still worked when it was unplugged and the CEL DID NOT come on...weird
test the resistance on the sensor while it is cold then again when its been warmed up to get a good idea if its reading correctly throughout its range.
It was the sensor the gauge still worked when it was unplugged and the CEL DID NOT come on...weird
test the resistance on the sensor while it is cold then again when its been warmed up to get a good idea if its reading correctly throughout its range.
- Status
