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Discussion Starter #1
what are the symptoms of a bad coolant temp sensor (ECU)?

My gauge works fine, I am curious to know how people know their coolant temp sensor for the ECU (green one) has gone bad.

I have a gen3 if that matters.

My car hesitates and bucks when building boost. I've replaced almost every ignition component other than my igniter (which I think wouldn't cause that problem)

The next thing on my to-do list is do a boost leak test.
 

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Discussion Starter #2
I've seen and searched a bunch of threads regarding this issue. I don't think it's suppose to throw a code?
 

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Are you getting a code?
It has happened to me due to:
-bad gas (took a tankfull and two days to disappear)
-water/moisture/oil in places where it should not be... it disappeared after a few hot days
Both of those problems had not very satisfying solutions because i did not DO anything... kindof unsolved.
yup, do a boost leak test.
I do not think your symptoms have to do with a coolant temp sensor...
 

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Discussion Starter #4
No code for coolant temp sensor.. i'm just asking cause I think i've tried everything else..
 

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Discussion Starter #5
has anyone replaced this sensor without getting a CEL and actually helped them?

i'm going to buy one at autozone tonight and see if it helps. I got quoted $30 or for the part over the phone. I'll report back if it cures my problem.
 

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if the coolant temp sensor is broken you will stay in open loop (cold start) and should run rich. I think if you have a stock gen3 and are using the turbo vsv you should also see the boost limited to the cold start boost which is 9psi. You can check easily to see if it is NOT the sensor by just unplugging and running the car, if it runs worse like cold start then the sensor was working properly if nothing changes it may or may not be the problem. I think the sensors are like 7.50 on ebay, it is a generic sensor you can get off most toyotas at the junkyard for cheap.
 

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Discussion Starter #7
i'll try unplugging it first before i replace it..

thanks
 

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Discussion Starter #8
I didn't even bother unplugging the unit since I had to remove a bunch of things to get to it. It's only $30.

I replaced my coolant temp sensor with a brand new $30 unit from autozone.

My car runs like a beast!! I just wanted to update my thread incase someone runs across this thread searching :)
 

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just got back from driving around town. No difference....I guess my coolant temp sensor was fine afterall.

My issue is my car will bog/hesititate if say I'm in 2nd gear going around 3k rpms and I give it 2/3 throttle, it will hesitate and bog until 4k rpms, then it'll go. Even then, I feel like I'm missing 25-30 horsepower.

I'm running gen3 electronics with ct20b turbo, intake, greddy PEX, greddy intercooler, blitz decat, 15-16psi. Fresh oem plugs, wires, 02 sensor, cap and rotor

I guess the coil is next to check.
 

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redmk2 said:
if the coolant temp sensor is broken you will stay in open loop (cold start) and should run rich.
thats what was happening with my mr2 when it needed a new coolant temp sensor/thermastat. the car would get horrible gas mileage sometimes. sometimes even if i let it run for awhile, it wouldnt go over the 3rd or 4th increment on the water temp gauge.
 

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update.

Played with my TPS sensor and I tilted toward the middle compared to where it was clocked a bit counter clockwise before.

Pros:
better thottle response
less hesitations and bogging
reading 20-21 inches of vacuum compared to 19 inches of vacuum

Cons:
idle went up from 925-950 rpms to 1100 rpm's (can't adjust any lower)

Wierd thing is when my headlights are on, my idle goes down to 950-1000 rpms.
 

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Update: I changed my coil and it helped a little, then I found the found my real issue....my timing gun was off by 4 degrees. Instead of running 10 degrees BTDC I was at 6 degrees BTDC. I found out by using a buddy's timing gun . My car runs like a beast now.
 

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Is there a part number for the green temp sensor? The pictures on Autozone, Advance and Orreilly's look like the black temp sensor.
 

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if the coolant temp sensor is broken you will stay in open loop (cold start) and should run rich. I think if you have a stock gen3 and are using the turbo vsv you should also see the boost limited to the cold start boost which is 9psi. You can check easily to see if it is NOT the sensor by just unplugging and running the car, if it runs worse like cold start then the sensor was working properly if nothing changes it may or may not be the problem. I think the sensors are like 7.50 on ebay, it is a generic sensor you can get off most toyotas at the junkyard for cheap.

Resurrecting this thread. My water temperature gauge does not move at all. Car is drinking gas like crazy so it must be running rich all the time. Bought a new sensor before reading this thread but can't get the old sensor our without putting in too much force and breaking things. Want to get the part it connects to just in case.

Does anyone know what the pipe/neck is called that the sensor attaches to or even a part number? It's a stock Rev 2 3sgte.
 

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Make sure that you change the correct sensor. The gauge and the ECU use different ones. In other words, if the gauge sensor is bad, it has nothing to do with how the car runs. You should consider that maybe the sensors are correct and it is actually the thermostat that is bad.
 
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