2001 s40 car accelerates and overheats
 

Panic call from daughter car is accelerating by itself up to about 2k rpm with foot off accelerator then it starts to overheat. She shuts off car and it is hard to start. what in the world is happening?! Car is 2 hours away cant check it until tommorow

After reading every Volvo forum known to man and reading any thread that sounded like this. I came to the conclusion that the engine coolant temp sensor had become erratic if not just short of errant. I drove the two hours after purchasing a new temp sensor and thermostat installed same and then drove that car the 2 hours home without a single issue.

That is good news. Thank you for the answer. I too have a daughter driving an old S40.

I just had the same experience on my 2000. What I noticed was that the temp gauge was showing a mid gauge reading on a cold engine, then when driving the gauge wandered eventually going into the red... Replaced the tstat and sensor and running fine. Now I need to figure out why I have a slow leak. Probably need to clean up the crush washer on the sensor :-( Suggest you keep an eye on your S40 as well.

Thank you for reporting back! That's a helpful thing to know.