Just purchased a few days ago and the car runs like crap, rough idle and almost stalls, overheats during stop and go traffic. i found a vacuum hose missing on the back of the intake plenum and plugged it so it runs slightly better. Problem is i cannot find where the hose is supposed to go and found electrical plug connectors not plugged into anything. So i just need to know where the vacuum line plugs into and what component is missing. See pics, thankyou
Further to this mystery, according to GM and other internet pics the vacuum line from the left side of the plenum goes to a cone shaped valve then splits into two smaller hoses, one goes to the drivers side by the master cylinder somewhere and the other goes to a wire coming out of the harness close to the firewall. I've searchedd and searched and cannot find the wire harness adapter thingy or an open port on the drivers side. The car does not have cruise and is a manual transmission.

 

Hi 87firebird2.8v6, welcome to TGO

At the back of your manifold, the capped off line is supposed to have a one way valve with two ports, one port connects via a vacuum line to whats jokingly called "the orb of power" around here by some, it's a vacuum reservoir that's shaped like a ball (about softball sized, as I recall) and is mounted under the battery. The other port connects to a small gauge hard plastic line that controls the HVAC system. Without those hooked up correctly, your HVAC will blow (mostly) out of the defrost only, which is the system's default for a no vacuum to the HVAC controls situation. I will enclose pics of what it's supposed to look like, as well as a pic of the charcoal canister, do you have one of these next to your air cleaner on the passenger's side?

 

ok, i appreciate all the info. I have the charcoal cannister but the vacuum sphere is no where under the battery...but i will look further tomorrow just to be sure. Could you possibly show me where the hvac hard line comes out of the firewall because that line is no where to be found on mine. Thanks so much

Also not sure if it is related but my vent controller in the car will not slide all the way to the right to select defrost vents, it stops about 3/4 way. i pulled the unit from the dash but cannot see a defect.

Cheers

 

I was unaware of this orb until your comment. When I turn off my car, it very quickly reverts to the "defrost" setting for vents. Is that normal for the system, or should it be staying where it was last set for longer than a few seconds?

My '89 wants to stall at idle, and I'm trying to decide if it is a vacuum leak, or just the awful gas I'm still getting out of the tank.

 

Hi 87firebird2.8v6, Believe it or not the hardline doesn't have it's own separate exit from the firewall, it's bundled in with the HVAC electrical harness that exits the firewall via a rubber grommet. Also of note, there are actually supposed to be two of those hardlines there, one that brings vacuum from the valve at the manifold to the HVAC control, and one that connects from the HVAC control to the heater control valve, to shut the coolant flow to the heater core when the HVAC control tells it to. If your slide lever won't move all the way then it's jammed somehow, I have not yet seen that failure mode so I'm not quite sure what to send you in there looking for.

Hi codyman125, Your's is absolutely leaking, or not holding vacuum. If I shut my car off at night, and then next morning move the HVAC lever from floor heat to defrost (for example) before starting the engine I can hear the vacuum servo move the deflector door. If mine can hold vacuum in the orb overnight, and yours only holds vacuum for a few seconds after shutoff, it's loosing that vacuum somewhere. Now whether the leak is bad enough to affect the idle is a simple enough thing to check, unplug the plastic valve in my pic, block the vacuum line at the manifold, and see if your idle improves. I would think a leak big enough to affect the idle should be a fairly large leak indeed, do you hear any hissing from the HVAC control head ?

 

That's what I thought I remembered from when I first owned this car. I haven't heard any hissing, but the line from the orb to the valve was completely severed (chewed through?) when I got the car back last week. I replaced that line, which got cruise and HVAC controls working much better.

The vacuum it holds is very inconsistent. Almost zero seconds at times, but it held for a few minutes last night when I was out for a cruise. I'm wondering if my check valve is the failed component, and it is working intermittently as it gets broken in again. I will have to try capping off the valve to see if that improves Idle soon! Right after I fix the newly leaking radiator...

 

you absolutely nailed it. I took the car out for a drive, and when I got home, there was a clear and obvious hissing from behind the HVAC controls. I just didn’t notice it before.

also a LARGE puddle of antifreeze. So that is moving up on the priority list now too.