I'm building up a car and just recently been idling the new engine. It idles between about 750-1000rpm, slowly moving up and down in speed, back and forth. Anyone know why? The engine's only lightly mod'd, header, CAI, and the EGR valve is removed and sealed off.

Is this something that's common for new engine installs, and will go away with time once the ECU "figures things out," or is it something more serious.

 

well, there is a big topic someplace on here about all the possibilities of the problem. Some say vacuum leak, some say fast idle or your eacv, but with mine it actually ended up being my ecu. Since i replaced it i dont have any surging problems. if i can find the link i will post it

 

Its usually the idle control valve on the bottom of the tb. Take the cover off and you should see a white plastic thing with a brass looking bullit in the middle (bad description, I know). Tighten the white plastic piece til it bottoms out. That should take care of it. If you need pictures of it email me.

 

my vote gets a vacuum leak, my 92 S did the same thing and the problem was a vacuum line, but it didn't do it all the time

 

Alright, thanks. I'll check out everything. It's getting close to being drivable so I'm getting a bit excited.