2006 s60R with IPD ecu software (I think). Car runs perfectly, smooth acceleration until normal operating temperature is reached. then I get mild surging/stumbling upon starting to move, and at cruise (60-70mph ). No noticeable rpm change or shifting of gears. same results when outside air is -30 to +30.
if I stand on the gas, it goes like a drag race car to any speed. I get no lights or codes. New throttle body, ignition coils, plugs, O2 sensor. Other sensors etc have been swapped from a working car with no change. It seems to me that something is sending the wrong codes to the ECU when temp preaches 190 deg. I would like to try a lower temp thermostat, but can't find one.

its driving me nuts and beating up my wallet.

 

Please don't post your question about your S60 in new member. That's just a place to introduce yourself and your car, not to ask technical questions.

 

Don't change the thermostat... Have you measured the resistance of the ECT? sounds like its going a bit off. Do you notice the temp gauge wandering or going a bit higher than in the past (a sign of the temp sensor going off). Also, if you are running an ECU, you may want to looking into adding a product like Redline's Water Wetter. It can help the heat transfer through the radiator so you an leave the Tstat at 190.