im getting a 91 convertible z28 black with grey leather power seats and windows and only 56,000 miles for $4,500 tommorow what all should i do to it first to get the most out of it its already got flows on it to what all things do i need to check and do when i do a tune up on it thank u

 

Do everything. Start from the top.

You must assume that NO maintenance has been done. Start with all fluids and filters. Engine and transmission oils and filters ($40), differential oil and additive ($15), coolant ($15), fuel and air filters ($10), PCV valve (AC only!), oxygen sensor ($25), vacuum hoses, compression or cylinder leakage test, etc.

Continue through the ignition system (NOT just spark plugs), and then the control system and adjustments, like cleaning the throttle body, and adjusting the IAC, TPS, timing, etc.

Once it's running right, continue with brakes, wheel bearings, steering and suspension, belts and hoses, exhaust, and body lubrication/adjustments.

Once you've performed all the required routine maintenance, you can assume that everything should be normal, and would cost you a total of less than $200 if you do the work yourself. Once the car has been returned to a "normal" serviceable condition, any remaining problems are a lot easier to solve.

 

Adding to what Vader said, its useless to mod your car if its not running right in the first place. Start by getting the car back into the mechanical condition it should be in. That in itself will probably be an adequate improvement. Then once this is done, the modifications you do will see much nicer, and more reliable results.