Tip & How-To about Saturn S-Series

Saturn S-series Starting Rough or Not Idling Well?

1991- 2000 Saturn S-series owners sometimes complain about rough starts or rough idling. In some cases it's a cause for the car not to start even though the starter is fine and the battery is at it's best. There is a simple reason for this that most owners don't know about.


So What's The Deal?

It's simply actually. It's called the Engine Coolant Temperature Sensor (ECTS for short). The what?! It's a basic thermoresistor (a resistor that changes it's resistance based on temperature) that is in a place where coolant flows past it. It tells the car's PCM (computer) how hot or cold the coolant is. Of course when you let your car sit overnight and come out in the morning to start it the coolant temperature is close to ambient temperature. When the car is started the coolant starts getting hotter and the ECTS tells the PCM the temperature as it's rising until eventually at full operating temperature.


Then What's The Problem?

Saturn used a plastic tipped sensor which is prone to cracking because of the constant heating and cooling cycles it sees. Coolant sees anywhere from -10 degrees Fahrenheit to 230 degrees Fahrenheit as does this sensor. So you can imagine plastic wasn't the best idea. It gets worse though. When this sensor cracks it allows coolant to flow to it's two wire connector and thus ruining the connector with old gunky coolant.


So This Has to Be Expensive and A Long Procedure To Fix...

Not at all! It's actually a very cheap sensor and in an easy place to replace. The nice part is that this was remedied in 2001 when Saturn switched to a brass sensor that does not have this problem. The part can be found at a local AutoZone or Advanced Auto or simply from you Saturn dealer (if one is still around). Ask for a Engine Coolant Temperature Sensor and when they come back check that it is brass (which is pretty obvious because the plastic tipped one has a very smooth rounded leading edge while the brass is more flat on the top).

The sensor is located just under and behind the upper radiator hose entrance into the head (might have to remove the intake tubing). It has a two wire sensor going to it. Check to make sure you're not changing the one that goes to the dash gauge on early S-series (91-95).

Remember to do this when the car is off and cold.

This should fix your rough starts and rough idling. If it doesn't, check the connector to make sure it isn't gunked up and put it all back together.

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2 Answers

idle is rough


Spark Plugs have to be changed every 3 years
Front Oxygen Sensors changed every 100,000 miles
Can't have any Vacuum Leaks -- anywhere on the vehicle
Need to have it road tested with a Professional Scan Tool
& look at all data & get caught up on Preventative Maintenance
Very few people change motor oil 3 or 4 times a year, if at all,
and the Variable Cam Actuators fail, as a result,that & few other
things can cause rough running engine & resulting idle issues
It's well known that Ford COP Ignition Coils fail sometime in
every year of ownership

Jun 21, 2013 | 2003 Ford Explorer

1 Answer

car won't idle sometimes and dies when i come to a stop. no check engine or service engine lights come on either. doesn't do it all the time though.


The idle is controlled by the idle air control valve, an electronic valve fitted on the inlet side of the engine, they get sticky and cause the car to stall. Sometimes they can be leaned and lubricated but in most cases a replacement is required.
To prove it is this valve, with the engine idling start turning on as much as possible, lights, stereo, heater, aircon on full blast etc.. the car should pick up on revs as these things are activated but your car will probably stall due to the valve sticking.

Nov 18, 2009 | 2002 Saturn S-Series

1 Answer

I have a 2000 Saturn L series 4 cylinder. The car starts up fine but sputters and runs really ruff when idle. When you start to go everything is fine, no problems.One mechanic told me it was a dead cylinder and the engine needs to be changed. Can anyone help? Do this sound like a problem anyone else has had?


scan check egr valve make sure its working. check plug wires and vacuum hoses +pvc valve make sure its not stuck open.bad or dirty fuel injections.causes rough idling.if all is good do a compression test to check for weak cylinders or low compression.

Jun 04, 2009 | 2001 Saturn S-Series

1 Answer

Rough Idle, and Black exhaust smoke.


coolant temperature sensor boken, check and replace if defective.

Feb 25, 2009 | 1991 Saturn SC

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