(SOLVED!) VERY rough Idle.

[SHObill]

vacuum leak.
As it begins to idle, the iab is able to keep up for a while, then it starts closing to lower the idle.

As it closes and the engine speed slows, the vac leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops...and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops... And the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops... And the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops and the iab responds by opening back up...as it opens...the engine speed increases and the vacuum leak begins...the iab responds by closing and as the engine speed slows down the vacuum leak stops

sound about right?

absolutely!

 

[rubydist]

When the TB is closed, the IAB is SUPPOSED to be the only way the engine gets air. Correct me if I'm wrong, but the IAB is not like VAPS. VAPS stays on it's current setting when you unplug it. IAB needs power to stay open, so when you unplug it, it closes and the engine should stall straight away.

fyi, on a properly running warm engine, it should idle, but slowly (around 500 rpm) with the iab disconnected from power, if the throttle stop is where the factory put it. the iab is not the only way it gets air, some still gets through the throttle plate.

 

[93rev2sev]

fyi, on a properly running warm engine, it should idle, but slowly (around 500 rpm) with the iab disconnected from power, if the throttle stop is where the factory put it. the iab is not the only way it gets air, some still gets through the throttle plate.

Yes. That's correct. Forgot about the throttle stop screw setting. To set that correctly, aren't you supposed to disconnect the TPS and plug the cruise control port though?

 

[jonheese]

Aha. So it was a vacuum leak after all. Testament to the fact that they can be among the trickiest issues to diagnose-- so many different physical places to occur and so many varying symptoms they can cause.

 

[nc89sho]

most shos i have ever seen <many> will stall as soon as you unplug the iab, but this one idled at 900rpm with it unplugged... that was the first clue.