my 1988 300 zx just got a tune up done and now it's pumping too much gas, what can the problem be

If it is carbureted, your problem could lie in the float bowl system, or internal to the carburetor. If fuel injected, the fuel pressure regulator could be bad, or perhaps an injector has failed. Either way, the tune-up should not be related to the problem unless something was accidentally damaged while it was performed.

EFI . And I have this same problem as soon as I have an answer I will put it up for everyone as its had me stumped.

Check the connection at the throttle position sensor. Connections should be bright silver, if they are green and mossy looking plug connector ,and tps will need replaced. Per Nissan. The bad connection tricks the ecm into believing its at full throttle,thus flooding. Fuel pressure regulator may be compromised as well it is located on the front of the engine just left of the distributor. Start the car remove the small vacuum line from the top of it if fuel leaks out regulator is toast. 65.00 plus tax auto zone. Hope that helps