I have a 1998 chevy 4x4 s10 blazer with a 4.3. When driving in slower stop and start conditions my engine will suddenly rev up to about 1000+ rpm (normally when it would shift back down to about 550 rpms). it seems to especially do this when at just over 5 mph and is only when it is in first gear after i let off the gas. I have no clue what this could be. Also when i am drive it is making a loud hummingish noise that only does this when in drive and not park. Any clues? Thanks

 

is i cold when he reving stuff happen..bcuz when my truck is cold.. it revs weird as hell.. but when its cold.. no problem.. my dads truck does the same thing when they are cold.. idk about if they r warmed up

 

No, everytime this has happened to me it has been after driving for some time, which really is quite weird.