94 Saturn SC2 - Idles goes up and down -- then won't start

WSCREATE

MEMBER
1994 SATURN

94 Saturn SC2
161,000 miles
4 cyl

Just "inherited" this car from my daughter as a pay back for a loan I gave her. The car seems to start okay and it seems to idle like a cold car would normally idle, I believe, about 1600 RPM. But, then, the idle seems to go down sharply to a normal idle of about 700-800, but it does not stay there more than a few seconds. The idle then begins to fluctuate between a high idle and low idle (800 - 1600 rpm) over and over again and does not stop the fluctuation at any time. When I push the accelerator, the engine does not respond. Instead, the car chokes and dies. And then it will not start again (engine turns over but will not start) until it cools down completely.

This car has a history of running hot, so I am told. I tried to check to see if the electric fan would work. Turned on the ac, but the fan does not seem to run when the ac is going or at any other time.

Someone told me to replace the ECT sensor (also called the PCM Temp sensor). However, I am seeking other opinions before I go buying parts for this old car.

Thanks.

4 Replies

PEPPERMRJ

MECHANIC
1,158 POSTS

Hey Ws,
Sure sounds like a ECTS (coolant temp sensor). They will effect idle speed, starting, and fuel economy to name a few. It also sends the data to the PCM for energizing the cooling fan. The AC has to be fully charged and operational for the PCM to energize the cooling fan. The link below is to the replacement procedure.

Get an updated brass tip model sensor from saturn. Should be less than $20.00. Be sure to check the pigtail that connects to the sensor. They can corrode internally. Clean or replace as needed. They are more expensive than the senosr so try cleaning it first.

Also check for vacuum leaks especially at the vacuum booster and pcv valve and hoses.

The cooling fan should come on at about 5/8ths to 3/4s reading on the temp gauge. The temp gauge on your year has a seperate sending unit from the
ects. The newer models use the same sensor.

https://www.2carpros.com/forum/saturn-sc-1-1995-vt4925.html?highlight=wolfman

Good luck and let us know. :)
peppermrj

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Monday, April 23rd, 2007 AT 8:52 PM

WSCREATE

MEMBER
59 POSTS

Thanks for the reply, peppermrj.

I replaced the coolant temp sensor today and lo and behold, the car idles like a champ. I cannot believe the difference that this $20.00 part has made in this car. This car was in a bad way, with starting problems, shutting off and not starting, fluctuating idle and poor fuel economy. Now, the idle is smooth as a rail and I have zero problems starting the car.

It was a breeze to replace. I made a nubie mistake by removing the temp sensor for the gauge. Found out the connector did not fit and got confused. So I took the sensor back to Saturn and they explained I had removed the wrong one. They showed me where the correct one is (below the other one and slightly to the rear). I removed the top radiator hose so I could get my wrench down there more easily. Overall, it was a piece of cake to remove and replace.

Yes, the new sensor has a brass tip. The old one had a crack in it. It appeared to have a plastic tip.

I will have to keep an eye on the situation with the fan. Now that the car is idling fine, I was able to let it idle for a good while and I found that the radiator is boiling over (actually, it is boiling over at the coolant reservoir). Interesting, but the temp gauge was only between 1/2 and 3/4 when it boiled over. I was running the AC part of the time, but not for a long time. Finding the source of this cooling problem is my next goal.

Thanks for all of the great suggestions. You were right on the mark!
:)

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Tuesday, April 24th, 2007 AT 8:09 PM

KCARTER

MEMBER
1 POST

This also fixed my car. My Fiancee drove hers like this for a long time. Couldnt ever figure the problem out. Replaced Idle Air control Valve, Throttle positioning sensor. It did the same thing, idle fluctuated would die when you give it gas. Found this post and bought the 10.99 part for it today and now it couldnt run better.
Tho this post wasnt directed towards me, thanks alot!

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Monday, November 10th, 2008 AT 3:37 PM

DAVID1998

MEMBER
4 POSTS

The CTS fixed my similar problem as well. An $11 part, 13mm long neck socket, and all of maybe 10 minutes. Saturn had quoted me 2 hours for labor - $275 -$325 for parts and labor.

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Saturday, December 26th, 2009 AT 2:09 PM