ok i need some opinions/help. The car is a 98 z24. When im driving, only over 80km, the car accelerates by itself sometimes, not for long, just maybe for a second. But it does it often. also over 80 my speedo goes up and down like crazy, but im sure its a bad stepper motor in the cluster, but that also started at the same time as my first issue. im going to clean my throllte body to see if that helps, but any other ideas would help. thanks

Can you hear it surge in the sound of the exhaust?