1999 Volvo S70

Throttle position sensor. With the car off have someone press the the gas while your looking under the hood. Look for the gas throttle cable coming from the gas pedal. Look see if there is any restriction that's keeping it locked up.

It may be a spring that's broke and not letting the pedal go back down.

Your ETM (electronic throttle module) could be the culprit. Although, the usual symptom is that the throttle will not work at all.