idle question

[DanDrath]

Once the cars warmed up when the cars in neutral it starts to rev up and down to about 2k and almost 0 and it keeps doin it. What would the problem be?

[Zwicked]

Run ECU diagnostics, including the heater o2 sensor test. This is the first place to start. Often hunting idle can be a bad o2 sensor, or sometimes vacuum leak. Also, is the base idle set correctly? If it's not or the AAC valve is dead it can do that.