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ECT Issue or Something Else?; Trouble Idling Cold
Topic Started: Sep 28 2017, 07:07 AM (211 Views)
acochran03
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I've searched and searched and hopefully starting this thread, we can better distinguish certain issues caused by engine coolant temp sensors (ECT) and maybe a throttle position sensor (TPS). Here's my story.

1996 3cyl 5spd has started giving me fits. When cold (meaning not at running temp) it simply will not idle. Either too low and it dies, or it will rev a little very sporadically on its own. Cracking the pedal just a tad it'll "idle" and warm up. Once warm, she runs just fine although mpg's are looming around upper 30's. Coolant level was 1/2 a quart low, but it's been like that for the 6 years I've owned it. It leaks or evaporates at a rate of 1/2qt per year. (No big deal to me) Not every time, but sometimes when cold, the rad fan kicks on as soon as the key is turned but prior to start. Also, the dash gauge functions like it has for 6 years. Never showed overheat, but goes to cold when cold and gets to about half way where she rides while driving.

Also, just to note. While driving there's a popping/clicking noise that fades in gets louder then fades out to quiet then back and it follows RPM's?!?!?

All this being said, on a 96, my impression is there's a 2 wire coolant temp sensor (Switch) by the thermostat that runs the rad fan, and a 3 wire ECT on the throttle body that gives PCM function and sends signal to the dash gauge.

SES Codes Pulled: P0117, P0118, and P0420

What is your expert's take on what's going on here?
Edited by acochran03, Sep 28 2017, 08:24 AM.
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geogonfa
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Just my .02ยข...
The computer has told you with the codes that the ECT is either failing, the connection to the sensor is not making contact, your ground wires at the back of the Intake manifold need to be cleaned/tightened, or the coolant passages flowing through the throttle body are blocked or plugged...
The coolant sensor (2 wire) in the thermostat housing only controls the radiator coolant fan,
the sensor (3 wire) in the top of the TB is for the computer and the temp gauge... :type

here is some good info:
[url]http://geometroforum.com/topic/5863680/1/

Note: my bad, when I looked at my phone I thought I read '95
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Edited by geogonfa, Sep 28 2017, 10:14 AM.
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freegeo
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If your car is a 96 then you only have 1 coolant temp sensor and it is located on the thermostat housing. It sends a signal to the pcm and the gauge. It is a 3 wire connector. You should check the connector and wiring at the sensor. There is a check that can be done to see if the sensor is accurate. Can you do checks with a volt meter?

PO117 and PO118 are both for the ECT sensor. Were those 2 codes checked at the same time? I don't recall anyone having a low voltage and high voltage problem at the same time.



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acochran03
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Yes, electronics technician by trade, so a voltmeter is no problem. What I guess eludes me here is the gauge reads normal like it always has, and if it's the same sensor, I'm leaning towards things downstream. I'll check grounds and probe around this weekend. Haven't had time to much more than plug the OBDII in last night.

P0117 and P0118 were read all at the same time.
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freegeo
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If you need the procedure for the codes I can post those.
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acochran03
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Procedure isn't needed for now I don't think. I'll have to look closer to confirm, and maybe the engine has been replaced, but I believe there's a 2 wire sensor on the t-stat housing and a 3 wire on the TBI. If that's the case then I'm also dealing with 2 sensors effing up which probably further justify a wiring/connection issue. I gutted all A/C equipment a month ago, and ran fine until this happened just last week, but we're also experiencing 50 degree weather that we didn't have then either.
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freegeo
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Are you positive it is a 96? Could you post a picture of the thermostat housing, that would be helpful. If it is a 96 and you have more than one ECT sensor then you have more problems than you might think.
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MR1 Kingsbury
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Exp. builder/rebuilder

A '95 engine with 2 sensors wouldn't fair to well in an OBD2 world...
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freegeo
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95 doesn't have a ect sensor or switch on the throttle body, but it does have 2 sensors. Your right though 95 wouldn't play well with obdii.
Edited by freegeo, Sep 28 2017, 12:35 PM.
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freegeo
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acochran03
Sep 28 2017, 10:12 AM
Procedure isn't needed for now I don't think. I'll have to look closer to confirm, and maybe the engine has been replaced, but I believe there's a 2 wire sensor on the t-stat housing and a 3 wire on the TBI. If that's the case then I'm also dealing with 2 sensors effing up which probably further justify a wiring/connection issue. I gutted all A/C equipment a month ago, and ran fine until this happened just last week, but we're also experiencing 50 degree weather that we didn't have then either.
The 3 wire sensor you are describing could be the TPS on the side of the throttle body. If you could posts pictures of the sensors it would help clear up some stuff.
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acochran03
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Sorry guys, I had to give it a wiggle and actually getting my camera behind the t-stat housing showed me that I was wrong. (According to the wife it happens pretty often) 3 wires are on the t-stat housing sensor. I'll start probing around today and see what I find.
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acochran03
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Upon wiggling wires to check 3 wire vs 2 wire sensor, the problem has been resolved and SES light has disapeared for another day. Runs just like normal now. Further inspection, and the connector pins are loose in the connector causing a bad connection.
Edited by acochran03, Oct 2 2017, 07:07 PM.
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freegeo
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Good to hear you got it fixed.
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