OK as title says I'm looking at a Cobra I found. Its a 99 black on black 112xxx miles on the body. Engine bottom is literally brand new 0 miles on it. Has the aluminum block bored .030 over with mmr 900 forged bottom end, pistons, rods, and rings. Crank is the factory forged crank that was polished. It has 8.5:1 compression ratio. a Built t56 6spd with about 10k miles. Has pacesetter longtube headers, off road x pipe with cutouts, flowmaster super 44s. 4.10 gears with ford racing trak lok diff. Has 03/04 cobra bumper. Stock heads and cams. But the car doesn't idle sometimes. It idled fine when I looked at it but sounded like a knock or piston slap was there. We didn't let car run but like 5 mins. It will not go over 40mph for some reason and needs a few min or touches to the paint but body looks great. I am getting the car for $3800 as it sets and getting a vortech v3 supercharger kit minus injectors that has 500miles with it for an additional $2000. Engine was built in Denver, CO buy a guy that does a lot of mustangs can't remember his name I want to say Ron. So want to get a bit it now or pass it up if you guys can help me deside. I know it needs a new tune on it and maybe a new IAC. That's all I can think that may cause the issue with idle not sure on why it won't go over 40mph or the knocking sound.