O2 Sensor fouling out

[sapix @ RHIT]

I have a 1990 Nissan 240sx (KA24E). Its running pretty bad. Its got a flat spot in the throttle around 3500rpm. The car is also missing most of its power. I feel like I've got economy car power and muscle car gas mileage.

I replaced the O2 sensor and the car ran better for about a week. The O2 sensor I pulled off was only like 4 months old. It feels like the car is missing.

Recently replaced parts:Timing Chain (Tensioner and gaskets and such also)Water PumpBeltsSpark PlugsDistributor Cap and RotorO2 SensorPCV ValveFuel Filter (6 months ago)Plug Wires (6 months ago)

Does anyone know what could be causing my problems?

Thanks

[navysnail]

it is running rich, check your maf

[sapix @ RHIT]

Thanks. I cleaned the MAF with the rubbing alcohol and the car is running much better now.