My 1987 300zx slowly over heats but doesnt have any leaks. That i know of. the coolant tank bubbles to the point where it leaks out and u can hear it bubbling. i replaced the water pump and i installed a thermostate but the thermostate made it over heat quicker. The hose from the radiator to the engine looks to be a lil swollen. Now about the bad idle problem. I replaced the spark plugs, wires and distributor cap and yet it still has a bad idle. it hesitates when i hit the gas and chugs. if i leave it to idle long enough it dies out. the whole response from when i hit the gas is very terrible. I was thinking it may be a vacuum leak since the air intake is pretty long and has alot of sections to it. Thank you