high idol in park/rpm surging

[nandosmontecarlo]

I have a 2003 monte carlo; it was running great until recently; i noticed that the car began to surge while driving like it was accelerating on it's own; when i got home and put it in park, the idol was very high (1800 - 3000); my neighbor hooked up an OBD ll and tried to scan it but wasn't able to run a scan; it stated also that it the car had history of any codes; we ended up just re-setting it by removing ground cable from battery - which we know isn't the solution, but this time it brought back to a normal idol; but now it started happening again with a high idol in park; so i tried it again but the idol is still high

[Schurkey]

I'd be wondering why the computer won't communicate with the scan tool.

Are you sure the scan tool works? Have you seen it talk to the computer in other vehicles?

[DrRadar]

Agree with Schurkey that it's best to get scan working. Hard to troubleshoot a computer controlled engine without data. See if a local parts store like AutoZone can read it. Having said that, throttle position sensor jumps to mind as possible failure. Seen that on at least two of my vehicles. But without data, that's just one BB from the shotgun.