Check engine light(coolant temp. always too low) and car is sometimes very hard to start?

Ok. I have a 97 Dodge Avenger ES with the 2.5L V6. My check engine light went on on thursday morning, and I took it to autozone that night to get it checked out. They said that the coolant temperature was always to low and recommended I purchase a new coolant temp. sensor. Since I didn't think it was urgent, I didn't buy it. I drove to another store and the light was still on, but when I left the store, it was off, and has been as of now. The next morning my car started fine, but after school it wouldn't start. I tried like 5 times, and I got it to start on the 5th time while holding the gas to the floor. I was wondering if the problems were related. There was one other time I couldn't start it well, but other than that fine. It starts PERFECTLY when warm, but a little slower(not much) when it is cold(milwaukee). Just those 2 times I had trouble.

Should I replace the sensor? Why would the check engine light go off now? Will it start fine with a new sensor? Also, I just purchased it, has 159000 on it, and I am going to run fuel system cleaner through it if that will help. Thanks

?2009-11-14T06:17:48Z

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Coolant temp sensor tells the engine computer the engine temperature so that it can make changes in injector pulse width and timing. If coolant sensor is bad it can cause all sorts of problems. Relying on Autozone's $7.50 per hour help to diagnose car problems is not usually a good thing to do , but in this case I think maybe they are correct. Replace the sensor.

Niklaus Pfirsig2009-11-15T20:45:39Z

A good mechanic should measure the actual coolant temp and compare it to the sensor reader on a professional grade scan tool. If the temp is higher than the scan tool indicates, that would warrant replacing the sensor. If the actual temp is low and matched the sensor reading, then the problem lies elsewhere.
The cold start problem indicates that it may not the coolant temp sensor. When the engine is cold, the ecu runs the engine in "open loop" mode, and forces the ignition timing and air-fuel mixture based on an internal table of preset values. When the engine warms up, however,the ecu calculates the mixture and ignition from reading taken from several sensors

Possible problems other than the coolant temp sensor are:

Vacuum leak or air leak between the air filter housing and throttle body,
bad thermostat
sensor creep in the IAT, O2, and MAP/BAP sensors (if so equipped
corroded or damaged sensor wiring.
bad plugs or plug wires

Kerrin2015-08-07T21:28:41Z

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Check engine light(coolant temp. always too low) and car is sometimes very hard to start?
Ok. I have a 97 Dodge Avenger ES with the 2.5L V6. My check engine light went on on thursday morning, and I took it to autozone that night to get it checked out. They said that the coolant temperature was always to low and recommended I purchase a new coolant temp. sensor. Since I didn't...

Anonymous2016-10-15T15:53:55Z

Low Coolant Temperature

Anonymous2009-11-14T07:17:09Z

The light will come on and go off periodically. That is normal. The coolant sensor tell the computer what temp the coolant is. That in turns tell the computer how much to let the injectors to spray. When the engine is cold it needs a little more fuel to run correctly. As the motor warms up the fuel is decreased until the motor is running at peak temperature. replace the sensor and your starting problem will go away.

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