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A stuck thermostat can cause those sort of symptoms. Anywhere from not getting up to temp to overheating in a heartbeat. Only way to test this, is to pull the thermostat and see if it is stuck open. If it looks OK, then you'll need to test its operation, i.e., drop it into a water bath, heat it up and see that it opens at the correct temperature.
There are also number of other possible culprits here. From a faulty engine coolant temperature sensor (ECT), bad electrical connection(s), faulty ECM, etc. Have to do some diagnostic work to rule these out one at at time, whatever is left is likely the true cause of the issue.
2002 Toyota Corolla S, 1.8L 1ZZ-FE VVT-i
2003 Toyota Matrix XRS, 1.8L 2ZZ-GE, VVTL-i (RIP)
2009 Toyota Matrix XRS, 2.4L 2AZ-FE VVT-i
2009 Toyota RAV4 Limited, 2.5L 2AR-FE Dual VVT-i