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1G 1990 Idle jumps around

SnowmanFD

Proven Member
102
4
Dec 11, 2021
North Seattle, Washington
Coolant temp sensor looks broken off in pic Can cause hard start high idle. Its by thermostat housing. Blue wire also unhooked by it not sure whats that too. The one the looks broken off should have a plastic connector that plugs into it. Id look the whole engine bay over fill the low fluids find out why low Safety first. look for any other broken sensors loose wires missing parts. Might be multiple issues causing it be I'd work on the cheaper and easier ones first.
Can the coolent temp sensor being broken off cause the car to not start?
 

steve

DSM Wiseman
14,415
1,364
Feb 3, 2002
St. Charles, Illinois
Can the coolent temp sensor being broken off cause the car to not start?

Yes. A disconnected ECT sensor causes the ECU to think it very cold out, like -70 something. The ECU believes it has to spray a lot of fuel to get some to atomize and the result is that the floods the engine.
 

steve

DSM Wiseman
14,415
1,364
Feb 3, 2002
St. Charles, Illinois

91Eclipse GSX

Probationary Member
16
7
Jan 6, 2017
ionia, Michigan
I believe steve is correct I was mistaken. The sensor you can see broken off in your pictures is the thermovalve. The ECT sensor is below it. But your symptoms very well could be a bad ECT. If the ECT broken off unplugged bad wires etc. Could all check out visually and still be bad could verify its faulty with a old scan tool. If bad make sure you get the correct one the communicates with ecu. There's 2 ECT's the other one is for the coolant temp gauge. The gauge in the car can read correct and the other one still be faulty. The one that could be causing your problem is the one the communicates with the ecu.
 

steve

DSM Wiseman
14,415
1,364
Feb 3, 2002
St. Charles, Illinois
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waltah

Proven Member
245
107
Mar 2, 2011
fairfield, Virginia
Yes. A disconnected ECT sensor causes the ECU to think it very cold out, like -70 something. The ECU believes it has to spray a lot of fuel to get some to atomize and the result is that the floods the engine.
I don't think that's at all likely though. I've had OBD I Expos start just fine with the ECT wires broken off at the sensor. They run way rich all right but they do start.

The ECT sensor can be checked in place with an ohmmeter. Look at the table in Steve's superb post and estimate the resistance for the engine temperature: If it reads close to that, look elsewhere for any big problem. The technology of these devices is such that tricky failures aren't likely -- if they work at all, they work well enough.

Snowman, if the car won't start go back to basics: Assuming nothing mechanical newly broken and that things like mixing up spark plug wires or moving parts that tell the ECU where the crank and cam are have not happened, you must have lost spark, fuel, or proper amount of air. If it even pops or stumbles some before dying then most likely the spark is okay and you've either got way too much fuel (you'll smell the gas) or way too little OR far too much air.

If it's really dead -- cranks fast enough but never even pops -- pull a plug, put the wire on it, and lay it on the head. Have someone else crank the car and look for a spark. Don't hold the wire while doing this unless you want a shocking experience.

If dead and you have a spark, think about something causing no fuel at all.

If it does try to start, spark is probably okay.. Think first about fuel. After cranking a bit pull a plug and look/sniff. It should be damp and have a strong smell of fuel.

If there is some fuel then an air leak is likely giving you a mixture too lean to start. All the vacuum hoses can cause idle problems (if off/broken) but I think only the one to the PCV valve will suck enough air to prevent starting -- check that one.

An air leak that got worse would cause all your symptoms -- first too high idle speed and maybe unstable, then in the end 'no start.'

Congratulations! You may now have a big problem with the same root cause as the idle speed issue. Big problems are much easier to find.
 

steve

DSM Wiseman
14,415
1,364
Feb 3, 2002
St. Charles, Illinois
I don't think that's at all likely though. I've had OBD I Expos start just fine with the ECT wires broken off at the sensor. They run way rich all right but they do start.

Stick around young Padawan, you'll get plenty of chances to see the broader range of behavior specific to the beast. If you're in a hurry there are many examples available using the force (search). :)
 

SnowmanFD

Proven Member
102
4
Dec 11, 2021
North Seattle, Washington
So update on my idle: i grounded my throttle body and the car runs all-around better and its fixed the idle issue.

I also did a boost leak test and found no leaks!

Anyways onto it not starting
I put some starter fluid in it yesterday and it started then it died (died on its own i didn't shut it off) so i know the issue is something that has to do with fuel my guess is the pump because, A. I no longer hear it prime when i go to start it and B. The previous owner said he installed an aftermarket one but wouldn't tell me much about it.

Here is the response i got (photo below)

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FYI: this dude doesn't know much about cars, and i never really trusted most of the things he said about it.
 
Last edited by a moderator:

SnowmanFD

Proven Member
102
4
Dec 11, 2021
North Seattle, Washington
Last edited by a moderator:
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