My freemotion 770 interactive treadmill is not running smoothly. It speeds up and slows down on its own at times

SOURCE: Proform Treadmill doesn't run constant speed.

You have a friction problem between your belt and deck. A treadmill of this age either came with a waxed deck, or requires periodic silicone lubricant spray on the deck. You can check your owners manual to see which type of surface your machine has. Typical belt life on a consumer grade treadmill is about 2 to 3 years. If you purchase a new belt from the manufacturer it will come pre-lubricated.

SOURCE: 2 1/2 Briggs......doesn't run smoothly....surges at all speeds.

Hi, Check that you have the correct spark plug fitted or fit a new one as it sounds like your plug is getting hot then shorting out.
Sometimes the magnito can do this as well. but I would start with the plug.

SOURCE: Treadmil stops or slows down upon walking.

Check both belts to be sure they are adjusted and not slipping.Check the underside of the walk belt to see if it feels frayed in the center as compared to the edges, the center always wears more than the edges a really worn belt must be replaced. if it is nor worn there is a wax lubricant for proform treadmills that can be purchased at retail stores that sell treadmills.Sears, dicks sporting goods and also treadmilldoctor.com are good places to buy it.

SOURCE: Treadmill won't slow down

if you look at the front roller. there will be a black device that has two wires. this is your speed sensor. Make sure it is facing the magnet on the roller.

SOURCE: I have a Proform 770 EKG Treadmill jerks and squeaks

The drive belt was loose. I tightened up the motor just a smidge using a crow bar. That solved the problem.