ok so im goin to try to explain this the best i can, this is my first car its a 1989 mustang LX hatchback 2.3l. i got it from my grandfather this cars has 120k miles are was rarely driven since 2003. me & ma dad are trying to repair all the probs we come across. here is my prob. when my car idles it does run smooths it sounds like im stepping on the gas then off then on then off idk why. then when you press the brake to goto drive from park, its like the engine sounds like it wants to a stop then gets back to idle & at the same time this happens the car like jumps forward like some1 pushed my car from the back. my dad said the engines isnt knocking or anything. idk what the prob is. the previous took the car to the dealer for all repairs. i already changed the oil. the same spark plugs & wires n stuff is still there from when this was originally made. he sai he always put 93 gas in the car i recently poured 5 gallons of 83 in the tank 3 days ago to keep it runing. idk what the hell the prob is but if you need more info or wud like me to upload a video of it ill glady do so.