Removed and cleaned throttle body, IAC, and deleted bellmouth.

It's been a productive sunny Sunday. I have taken off the throttle body assembly, cleaned the idle air controller (IAC) and reassembled it, without the bellmouth.

The IAC is a common cause of rough idle on the 3.8 Buick engines, as it can clog up with carbon and dust deposits. Mine was filthy. I cleaned it all out, including the butterfly valve with spray-degreaser and a rag. The IAC needed to be removed for cleaning, and the O-ring was still servicable. The idle air controller is a computer controlled valve that lets the correct amount of air into the plenum for idle. The computer automatically adjusts it to maintain the correct idle speed when load is put onto the engine, for example, putting an automatic into drive, or turning on the air conditioning or headlights.

The bellmouth is a piece of plastic which sits inside the plenum, helping distribute the air evenly between the cylinders. When it is installed, it causes the inlet tract to taper, reducing it's diameter by about 10-15% after the throttle butterfly. This bellmouth was not fitted to series 1 VN Commodores, but it was fitted to all models after, up to the VR. It was designed to smooth idle slightly, as without it the rear two cylinders experience increased air-flow and tend to run leaner, and it was apparently also designed to correct a "problem" of excessive wheel-spin off the line. This bellmouth has been removed from my car. I have heard that a memcal is available that maps the idle mixture to be slightly richer to prevent the leaning out of the rear two cylinders, and I will be doing this as soon as I make my Delco unit programmable via Kalmaker or something similar. Unfortunately, it is not possible to adjust the output of the injectors individually with this system, as they are connected sequentially.

I got a bit of paranoia about using the correct gasket sealant, as I normally use Loctite No.3 Aircraft non-hardening gasket sealant, but I have heard that the incorrect use of silicone based sealants on engines with oxygen sensors can cause the sensor to fail. I have no idea if this Loctite stuff uses silicone, but I had a look at the guide on the Loctite website and it says it is okay, so I reused the old gaskets which were still okay, and put a layer of gasket cement on each surface. Apparently the gaskent sealant can be used without paper gaskets, but I'm just not game to do that somehow.

I also adjusted the trasmission kick-down cable, as it was not shifting down easily enough on throttle application. I tightened it, only too much, and this caused the transmission to hold the throttle open when coasting, which can be quite un-nerving. Only tighten it one notch at a time.