hey there im trying to figure out what this part is as well what it does
the plug on the bottom right of the picture, when plugged in causes the car to surge like rev to 2000, then back down then rev to 2000 then back down very rapidly... any ideas? thanks

 

It's a pic of your BAC valve.
That plug is FOR the BAC valve.

The surging it most likely due to a out-of-spec TPS.



-Ted

 

I second the call on it being a BAC valve

 

like you REALLY need to sacond ted...

 

yeah its the bac valve..like reted said the surging idle is most likley a tps prob.. but that bac valve could need to be cleaned or outta spec too

 

"Bypass Air Control" valve. Ok now what does it do?

 

It bumps up the idle under electrical loads when the idle would normally drop.

 

allows air into the intake based on what the ECU thinks the idle should be at (dependent on engine coolant temp, air temp, intake temp, timing, etc).

 

so what would cause it to cycle like idle to 2000 rpm then idle then 2000 rpm, over and over when i have the plug plugged in on the BAC
is it bad to drive without it plugged in?

 

i have a spare bac off an 88 n/a for sale

 

Keep the BAC plugged in. Set TPS.

 

try cleaning the BAC, make sure the gaskets are good, use gasket paper to be safe (i used gasket maker and it got sucked in =(

set the TPS as others say, and also check for vac leaks

 

blok it off

 

Listen, there are 2 ways to adjust idle on your BAC, there is and allen head screw on the end that the plug is pluged into, and a flat head screw on the opppsite side, adjust those and you will most likely solve the surging idle it did mine!