1988 chevy cavalier rs idleing and driving issues

k so I recently bought this cavalier about a week ago its and 88 automatic trans with 1.8 4 cylinder I thing not that it matters much. I noticed the exhaust had a smaller pipe from the manifold and the rest was strung with a bit bigger pipe and was attempted to crimp the pipes togather it was loud so I crimped thhe pipes better and used exhaust glue to patch the holes it runs better now to a point. but when I start the car it revs up a fair im guessing 3 grand since I have no rpm gauge but then it dies down to a low idle to the point were the car shakes a little bit. with the exhaust fixed I can get it up to 20 kilometres an hour with my foot off the gas when I turn fully it wants to lurch ahead/backwards. when I took it out for a highway drive today I came to a stop sign so I slowed and stoped and the car stalled out. started no problem. but I also tried later putting it in neutral and it doesn’t stall as I role to a stop it doesn’t shake in neutral. I would like to have this fixed but I need some pointers as of were to look. im not sure if this means anything but when I got the car it had a bad enough radiator fluid leak at the hose meeting the heating car on the engine side of the fire wall I repaired that and no longer leaks. any sugestions on what I could do do fix the lurching and staling.

@weliketodrivefast

Clean the throttle body first

If that doesn’t help, the idle air control valve is probably defective

Make sure you don’t have any obvious vacuum leaks