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!

Alfa GTV6 Rear Coolant Hose

 

There’s nothing like the mesmerizing sound of an Alfa Romeo GTV6 on the open road. When you’re behind the wheel, you never want to stop—especially for that dreaded "B" word: Breakdown! I’ve owned my GTV6 for 39 years, and it has been impressively reliable. 

Still, I've had a couple of close calls that almost left me stranded. One was an alternator failure. Fortunately, I made it to a friend's house and avoided being stuck. The first incident, though, was the rear coolant hose coming out of the left cylinder head, leading to the "T" fitting and feeding the heater core.  This burst, spewing coolant and a huge cloud of steam and ended an enjoyable drive. Luckily, I was able to splice the hose together and make it home, avoiding a huge tow bill or overheating and damaging my engine.

My advice to anyone who owns a GTV6 is to inspect and replace this hose before it leaves you stranded.

Alfa Romeo GTV6 Rear Coolant Hose

Can you see the rear coolant hose? In the picture, it is the hose located just to the right of the fuel inlet hose.  This rear coolant hose feeds the heater core and comes out of the left cylinder head and is buried in the valley between the two heads.  As you see, this hose is obscured by the intake plenum, the fuel inlet hose, and wires.

This hose is buried behind the engine and pressed against the firewall. It’s easily overlooked when inspecting your engine. As a result, it often becomes old, neglected, and frequently soaked in oil—making it prone to failure, possibly on your next drive.  

This hose is difficult to reach with the intake plenum installed; removing it may help. Once the plenum is off, you might as well inspect your intake pipe couplings. Note: A lot of coolant will leak out when removing this hose, so have plenty of rags around.  Ideally, you should drain a good portion of your anti-freeze out before removing this hose.  Don't forget to bleed your cooling system. The link at the end of this post on replacing the thermostat has tips on bleeding your cooling system.

The Alfa part number for this hose is 60701345. It’s a hard-to-find part, so check your preferred Alfa vendor, eBay, or bring the hose to match at a local parts store. The GTV6 alloy engine does not like overheating, so while you're at it, consider replacing all your hoses. The worst things you can do to a Busso engine are to not change the timing belt, run low on oil, or overheat it.

Alfa Romeo GTV6 Coolant Hose T Fitting

Inspect your "T" fitting. Mine had some corrosion.

So I soaked it in Evaporust.

Rust removed and ready for paint.

If you can't salvage your "T" fitting, the part number is 60533669.  Note that these fittings are subject to deterioration, and because they have two different hose sizes, they are not easy to find locally.  So it is a good idea to get one and have it in your spare parts stash before you need it.

Don’t forget the two thermostat bypass hoses up front behind the thermostat housing. These are also out of sight and frequently neglected. Read more about them here:

Alfa Romeo GTV6 Thermostat Replacement

Smooth sailing and happy motoring!

Disclaimer: 

This post is provided for informational and entertainment purposes. If you have any doubts about your ability to perform this work or have any issues, I recommend having it done by a professional. I am not responsible for any issues arising from your reading this post. Use at your own risk.