Alfa GTV6 Idle Speed O-ring

 

The Alfa Romeo GTV6 is filled with unusual and interesting engineering features and solutions. One of the unique features is this simple O-ring. This humble O-ring plays a big part in how your car runs because it regulates the amount of air that bypasses the throttle valve, setting the idle speed on your GTV6. If it is worn out, it will make for the most frustrating driving experience. If you are unfamiliar with the GTV6 Idle Speed O-ring, stick around —we'll tell you everything you need to know.

The Alfa GTV6 uses the above fittings to control your idle speed (minus the extra O-ring shown).  The various fittings are put together and screwed into the side of the throttle body. Over the years, the rubber O-ring can harden and become brittle, and when that happens, your car can develop idle issues. This tiny O-ring is often overlooked, and if you or your mechanic don't know about it, you can end up chasing all sorts of false solutions trying to fix your problem. 

If you have an idle issue or can't adjust your idle and don't have a vacuum leak, look into replacing this O-ring. The good news is the o-ring is inexpensive and can usually be had at your favorite Alfa Romeo vendor. It is also easy to change. 

  

Alfa Romeo GTV6 Idle O-Ring part number 60523368 size:

• 14 mm outer diameter 
• 7 mm inside diameter 
• 3.5 mm thickness

When you inspect your Idle O-ring, it should be soft, flexible, not oil-soaked, and not cracked. If it can't pass the inspection, you need to replace it. If you can't find a replacement O-ring, you can use the above dimensions to source one in an emergency.  Because of the heat and fumes in the intake tract, look for an O-ring made from a material like Viton rather than the more common Nitrile. 

This is the GTV6 idle bypass adjuster assembly.

The O-ring goes in first. Push it all the way into the hole. The O-ring bottoms out against a tapered flare shape.

The idle bypass assembly is then inserted into the hole in the throttle body. For clarity, I placed the O-ring at the entrance so you can see where it goes. Make sure you push the O-ring in first, as was mentioned above.

A close-up shot of the idle bypass assembly.  You should use a new copper washer at some point, but a little grease on the threads and washer will help it seal.

It is called an idle bypass because idle air bypasses the throttle valve.  The throttle valve on a GTV6 is nearly fully closed at idle. Idle speed is controlled by the amount of air passing through the above hose and bypass assembly. 

This air is drawn from the intake boot after passing through the airflow meter. This ensures the change in engine air intake, as controlled by the idle bypass screw, is sensed by the airflow sensor, which also proportionally adjusts the injected fuel rate. 

Note: the above image is from an early (1981-1983) North American spec GTV6.  Later GTV6 models with the EZ-L Ignition System (1984 and up, North American GTV6) and cars sold in other markets have their idle speed adjuster mounted on the side of the plenum assembly, as shown below.

How to Adjust the Alfa GTV6 Idle Speed

NOTE: To adjust the idle on a GTV6, DO NOT touch the throttle valve stop screw.  Use the idle bypass adjuster ring (red arrow).  The engine must be at operating temperature with no accessories engaged and the gearbox in neutral.

1. First, loosen the idle speed bypass adjuster lock nut. This is the nut to the right of the adjuster ring in the image above. You should hold the adjuster ring with another wrench while loosening the locknut.
2. Turn the idle speed bypass adjuster ring in or out until you have the correct idle speed. You will feel the rubber squish as you tighten the adjuster. When you have the idle speed set, tighten the lock nut while holding the adjuster ring to keep it from moving.  GTV6 idle speeds are listed below for your convenience.

1981-1983 Alfa GTV6 Idle Speed North American Specs

• 800-1000 rpm

1984-1986 Alfa GTV6 Idle Speed North American Specs

• 950 +/- 50 rpm up to 4,000 ft. elevations
• Above 4,000 ft, 800-900 rpm acceptable

How the Alfa GTV6 Idle Speed O-ring Works

This is the view of the GTV6 O-ring looking through the bypass adjuster. Notice the size of the opening through which the intake air flows.

 

A close-up of the idle O-ring opening at its maximum size. The more air flowing through this opening, the faster the car will idle. Remember, the airflow sensor meters the air, ensuring the correct air/fuel ratio. Idle-speed adjustments do not affect CO measurements.

 

Note the size of the O-ring opening when the adjuster is tightened down. Tightening the adjuster squishes the rubber O-ring and reduces the opening size, and decreases the idle speed.  This is why the O-ring needs to be soft and flexible.  Old school engineering. Simple and effective.

So the next time you place an order for Alfa parts, have them throw in a replacement O-ring.  And when it's tune-up time, replace it.  Having one handy can save you a hassle and keep your car singing its happy tune.

Smooth sailing!