Engine Performance problem
1990 Nissan 300ZX 6 cyl Two Wheel Drive Automatic 76000 miles
My 300zx twin turbo is running rough. When the car is in park, revving the engine sounds great from below 1000 up to 6000 RPM. When it is in drive however, between 1,500 and 2,5000 RPMs the car shutters a bit, stutters and sounds as if it will stall out. Above 2,500 it sounds and runs fine again. When slowing down, when the engine drops to 2,000 RPMs it starts to shutter again and has little power when the gas is applied again to speed up.
Last time I took the car in, they said the fuel injectors were clogged and cleaned them. It seemed to improve for a month and then it went back to the problem listed above. I tried the injector cleaners from Autozone but that didn't help.
I would think the injectors, once clean, would tend to stay that way unless some other force is acting on them. What is contaminating the injectors? Dirt bypassing the filter, interior lining of the flexible part of the fuel line deteriorating, injectors are just bad? Something may also be wrong with the spray patterns of the injectors due to deposits that just aren't coming off during the cleaning process. Also, is the problem you are having due to injectors or perhaps something else like a worn air flow meter or poor fuel delivery or pressure or a vacuum hose off or split somewhere. Also what condition are the ignition components? Diagnosing misfires on pre-OBDII cars can be tough, but if we are methodical in our efforts, and check off the " X" factors in the equation, we will eventually find the solution.