My 1999 V70 Wagon will turn over but not idle. It appears as if the throttle become disabled after it starts. I can gun the engine upon turning the key, rev it up to ~5000 rpms at which point the throttle seems to fail. If I turn the key again without removing it completely the engine will not turn over but if I remove the key and turn it again the engine will turn over but immediatly stall...

 

Sounds like an immoblizer issue.