99= OBDII= two O2 sensors (at least) One before cat, one after. If there is/are no cat/s Then the computer is probably freaking out and sending very little fuel to the engine to try and keep the exhaust as clean as possible. Now if the computer has been tricked into thinking it is getting a good O2 sensor reading from all O2 sensors, then it should run ok. But I highly doubt that anyone put that much thought into it.