car starts then revs high rpm and wont come down

 

check your fuel and your air check for vacuum leaks

 

if you would really like answers that would help you and avoid flames give following info when you post: year of car, n/a or turbo engine, stick or slushbox. Most of us can tell by the year what model you have ie 85T is a turbo z31. Z cars come in many flavors
and they are all different. example 84,85,86 Z31's pretty comparable. there were changes in 87,88,89. in addition 300ZX can refer to two completly different cars the Z31 and the Z32. No mindreaders here the more info you can post the most likely you get a
cogent useful answer