When applying brake,engine goes to full throttle,kept brake petal pressed hard.Goes back to normal after about 15 seconds.

Vehicles have what is known as a TPS Sensor. Throttle Positioning Sensor. When these go out you will experience these kind of symptoms. The vehicle is confused on how much throttle to give the car. It's not the way it was a long time ago - that cable from your gas pedal connects to the TPS and when it goes out that's what happens. Other symptoms will include dying on takeoff, smaller surges - going over a speed bump for instance - you'll hit the brake but the car will surge. If you've noticed any symptoms like that, this may be where your problem is. You have to get the car scanned by someone with a code reader. You can purchase the small, standard code reader from Advance for around $50 - which isn't cheap...but neither is getting a car that won't start to the parts store or garage for them to run code - and I can walk you through reading the code. It's literally plugging it in, turning the key on and then reading/resetting the codes. By scanning - if it's your TPS it will usually have a code.

Sometimes, though - like with a Ford Fusion - the problem is so short lived that the computer doesn't store the code for future reference because the system looks at it like an anomaly - that is, not a big enough problem to call home. In this case - you'll have to have a little bit better of a scanner - one that will read in real time. SO you can plug it in, drive around and if the problem pops up - you'll see it before the computer throws the message in the trash. Here's what the standard pocket scanners look like -
All The Best, Justin Lee 17 South Industries, LLC
Actron PocketScan Plus Code Readers CP9550