I've got a problem with motor reving up

[bowhunter260]

Everytime I engaged the clutch my motor revs up to about 4000 rpm and when I release it in a gear it goes back down. Even when I have it in neutral and clutch disengaged it idles at around 2500 rpm for about 5-10 seconds, then goes down to normal idle. I dont know what it could be, someone told me it might my mass air meter but I dont know. Any help would would be great. Thanks.

 

[bowhunter260]

No I have never cleaned the plenum, but I will and check the other areas. Thanks for the help.