Apparently my Civic saw Fast and the Furious once too many times. At idle especially, and sometimes in drive and reverse, the car will sit there and REV itself by about 1000rpm. It seems to happen more once the car is warmed up. The car also seems to have a very high idle when it is first started. (About 3000) I have no idea what the problem could be. We recently completed a block swap and the car runs very well other than that, the only thing I thought it could be was maybe a vacuum line in the wrong spot or something. Does anyone have any ideas? Thanks

 

check the deflection on your throdle cable, also get some seafoam or carb cleaner and clean your IACV

btw only post once, there is a button called New Posts at the top of your screen, alot of people use that and they dont like seeing more the one post about the same thing

 

It's definitely a vacuum problem, but it may not be in a vacuum line.

Check the seal around the brake booster (Round thing on drivers side of firewall) to see if it is leaking...

A buddy of mine had same problem, we couldn't figure it out. We knew it was a vacuum leak, but we checked and re-checked every vacuum line. Turns out it was the seal around the brake booster...

Check it out!

 

Thanks for the posts guys, I'm about to go in the garage and try everything possible to fix this. I need to get emissions tested by tomorrow or I can't get license plates, ever. lol

Could it possibly be the timing? Remember, it revs in drive and reverse too... could it still be the IACV causing this?

Thanks

 

this may help you narrow it down.

http://www.ef-honda.com/ben/Badidle.php

 

Checked everything possible, everything looked right... so I decided to pull off the TB and check the IACV... looked pretty clean, then I noticed the inside of it was rattling. Remembered I had an old Del Sol TB, so I pulled the IACV off of that one, and sure enough, no rattle. So, swapped the IACVs, at this point I'm 99% sure that had to be the problem. Waiting for some gasket maker to dry, so won't know til morning, though.

 

you may also want to look into the TPS as well. when my throttle positioning sensor went out, my idle bounced for no apparent reason. swapped it, and problem was solved...