Dies when goes in gear and made a knocking noise?

[littleblack84]

Hey guys Im new to the site and new to these kinda cars, been jacking with Mustangs my whole life. I picked up a 84 t type with a 86 motor in it and been working the bugs out of it, It started to make a knocking noise one day coming from the top end and I let it set for a couple days and now the noise is gone, I was told if the car sat for awhile (witch it did) it may of gotten a piece of trash on the lifters? and the 2nd problem Im having is when you crank the car up it does kinda idle high but goes down and idles fine but when you go to put it in gear it will not stay running incase you put your foot on the gas to keep it idled, the rpms drop alot, Any ideas?

Thanks again,
Jeff