So my early model 2004 S40 is having some issues.

When the car is cold it cranks perfectly fine. As it starts to heat up the throttle basically sticks and RPMs jump, right as this happens the thermostat says the temp goes all the way up and the warning light comes on. I know the car isn't overheating as it'd be impossible to have this happen within 30 seconds of car being on.

When I shut the car off it will not restart for a long period of time after this happening.

Could it just be something simple like the thermostat is jacked up and causing the RPMs to jump? Or what could it be?

Thanks for help. I tried doing some searching but couldn't find anything that sounded exactly.

 

most likely its the ECT (engine coolant temperature) sensor - the one right under the thermostat housing (follow the top radiator hose to the block and its the plug right under the cap).