Another Idle Surge question

[funkbuster]

hey guys, I just picked up a 1991 GVR4, car Idle surges, not a big deal, but wanna get it fixed. It does it pretty much all the time, warm or cold, but if I come to a stop and hold the brake pedal down, it will stop surging, which makes me think it is a vacuum leak. I had a 93 Talon that idle surged about the same and it was a vacuum hose missing, but I cant find one missing on the Galant. any ideas?
thanks
Chase

 

[eagle_talon90]

Try doing a boost leak test first of all. Here's a good site about idle surge that may help. Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge) Lots to read. But it helped me out a lot.

 

[DRAGIN]

The most common and most overlooked cause of idle surge is the BISS (Base idle speed screw) o-ring dries out and air leaks by the adjuster. You can buy them at Mitsu for dirty cheap.

 

[LASER4G63T]

Yes, definitely do a boost leak test. I found a nice hole in my IC

 

[ShawnsGarage]

If applying the brake stops the surge id say a vacume leak is causing this.

 

[funkbuster]

update, was driving car, came to a stop, and it was idling really low, sounds like I have big cams, hop out, look under hood, and BISS is missing, so I am like, good, that must have been the surge issue, so I cover the hole completely, and it still surges, I found a bolt to fit in the hole for the time being because car wont stay running when cold without something in the hole, but still surges.

video of it with the biss missing
YouTube - 1991 Galant VR4 exhaust clip 2