I have an 87 GL wagon 4wd with a hitachi carb that I can not get to idle right.

 

Checked and replaced all vacuuum hoses, triple checked all vac motors, all are good, egr is working(not creating vac leak), put in new manifold gasket, rebuilt carb and installed new base gasket...and I can not find the vacuum leak.

 

The car will idle at 1000rmp at 15 inches of vacuum, but any lower idle speed causes it to surge, and vacuum goes down to 10-12 inches. At speed the car runs fine. I also installed new coil, plugs, wires, cap and rotor.

 

I decided to recheck everything, and make sure float is adjusted properly(it is) and while checking I noticed that there is a thing called according to the vac diagram under the hood, an AIR CONTROL VACUUM VALVE.

 

What does this thing do, it has a connection to a port on the top of the back of the carb, a connection to a top port on the front of the carb, and a connection to the air cleaner housing, the other connection which was whacked was the vacuum connection which receives its vacuum from manifold vac thru a solenoid.

 

The port where this vacuum connection is was broken and somebody poorly superglued it together effectively closing the vacuum port and rendering it inoperable. Any ideas on what this does, could I just remove it? Or is this the cause of my bad idle(still runs bad with VAC port blocked shut though)??

 

bigtrout

I don't know about the carb models but the air control valve on the spfi is used to bypass the throttle during startup and idle and such. It seems to me you shouldn't have one of these if your running stock carbed. Maybe its been switched from spfi to carb sometime. Somebody else needs to chime in here I think.