Help! What Vacuum Hose Is Supposed To Connect Here? (photos Inside

ibcleeby · August 7, 2011

First, the short and to the point version:

2008 Acadia SLT2 with 90,100 miles on it. I have a vacuum leak and found this hose connection point behind the manifold on the passenger side of the engine with nothing connected to it (see pics). There isn't an obvious line anywhere I can see. Can someone point out what this should be connected to?

All the details:

Two weeks ago while sitting at a stoplight, my check engine light went on, as well as the *ding ding ding*'service stabilitrac/traction control off' messages and light on the display. Odd thing was that the stabilitrac error would disappear as soon as I accellerated away and then come back on when I let off the gas for a few seconds. Wherever I went, the stabilitrac would be fine while speeding up and then disingage again whenever I was slowing down or stopped. I have a code reader and found codes P0171 'system too lean (bank 1)' and P0174 'system too lean (bank 2)'. When I cleared the codes, the stabilitrac error would also disappear. The engine would also idle rough, but seem to run fine once the vehicle was moving.

After doing some research online, I changed the MAF sensor (the most common cause for those error codes). I also replaced the air filter, cleaned out the throttle body, and inspected the rubber air intake sections for cracks while I had things apart. Everything appeared to be in good shape. Unfortunately, there was no change in the engine performance or error codes.

Frustrated, I researched some more and determined I likely had a vacuum leak somewhere in the intake manifold. I did another inspection of all of the visible lines, rubber parts, and plastic parts. Everything was tight and in good shape. Finally, while running the engine, the cooling fan kidked off and I heard a slight sucking/hissing sound from the opposite (passenger) side of of the manifold. After spotting a small protrusion on the back side, I slid my hand behind and placed my finger over the end. I felt it pull suction and immediately the engine idle smoothed out and purred along like normal. Eureka - I found my leak!

Unfortunately, I can't seem to find a loose hose end anywhere to plug back in to the connector...at least not from the top of the engine compartment. I'm hoping that someone here can point me in the right direction as to where this spot connects up. In the meantime, I have placed a temporary cap over the stub to stop the air leakage. After a short drive this afternoon, no errors, lights, or codes.

Thanks in advance for your help!

Doug_Scott · August 7, 2011

Was the nipple as clean as it appears in the picture? If so, then it must have had a hose or cap on it. What is the sensor right below it, you can see the mounting bolt holding something black onto whatever that gray/dull-silver looking thing. Maybe if you backup a bit and took the pic again we can get some perspective on what we are seeing?

redvett · August 9, 2011

The Astro Vans never got away from vacuum HVAC controls so i would look for a thin plastic tube comming from the HVAC housing at firewall.

ibcleeby · August 12, 2011

OK, mystery solved...there's only supposed to be a rubber cap over this port . I coaxed one of my neighbors down the street to lift the hood on his Acadia and we took a look. I wonder why the port is there?

redvett · August 12, 2011

GM builds engines for many vehicles and that one went into S10, Astro & full size trucks along with industral equiptment several of which need a vacuum port.

OK, mystery solved...there's only supposed to be a rubber cap over this port . I coaxed one of my neighbors down the street to lift the hood on his Acadia and we took a look. I wonder why the port is there?