Stumped! need some help on this one!

[Damon318]

Hey everyone, ive been looking around on the forum and havent found any problems like this so if you know of any please send me in the right direction
so here it is, when im driving over 30 mph,let off the gas and just coast my rpms slowly go down to about 1000 (ust as they should)but if i coast long enough my rpms will drop to about 600 and then shoot back up to 1000 and just bounce like this every few seconds until i give it more gas. it doesnt die and it doesnt happen every time, its about half the time. i have no codes and have replaced the crankshaft sensor 5 months ago.
any ideas?

 

[Whiplash Performance]

You should take a look at the IAC motor. Try cleaning out the throttle body.

 

[Damon318]

i pollished my TB last week and replaced the IAC.
i just got back from autozone and i got an evap Po4040 code the guy said it could be the gas cap haha i am getting a new one. i really hope this is a $10 fix that would be wonderful!

 

[TheOtherNick]

Did it just start after you ported the TB? reset the pcm if it did.

 

[Damon318]

yea it started just fine. why should i reset my pcm? and how do i do that? just unplug the fuse?

 

[Bio248]

unplug the battery for like 20 minutes.

 

[Damon318]

i unplugged the battery to reset my codes. still no improvement. im thinking i might have yet another vacuum leak? so im going to start looking again. any other ideas?