Okay, so this vehicle I have serviced a few times for a co-worker. They just called me half an our ago saying they were driving and the car just started going faster. The person had to use full on brakes + parking brake(not clear if they shifted into Neutral or not, apparently it 'sounds' like that didn't help). What could this be? Stuck pedal or broken throttle linkage? I haven't seen the car yet but want to get an idea of if it's something I can tackle or not before attempting. I already advised not to drive the vehicle, obviously. I recently changed the oil and did a transmission fluid drain 're-fill'. The person also mentioned the pedal came back up but felt 'different'. They also heard a loud pop. Any ideas? Thank you!