Replacing idle screw O ring on a Mk1 Golf

This is for the 1.8tl JH injected engine. The O ring surrounds the idel adjustment screw on the throttle body and servers 2 purposes. First it creates a seal around the screw and 2nd it helps hold the screw in place with friction.

Approx. time: 5mins
Approx. cost $1 (plus postage)

When to replace:

Idle speed decreases over time (screw is 'rattled' out)
Engine idle is unsteady (vacuum leak - see video below)

Example of a 'flat' worn O ring that needs to be replaced.

Worn O ring on a Mk1 Golf idle adjustment screw.

You'll need

A new O ring, like this one.

How to replace the idle screw O ring

Take note of the screw's current position - how far it is screwed in (I took a picture with my phone). Then, simply unscrew the idle screw. It is about 2 inches long. If the O ring needs replacing it will either be hard, cracked or flattened. Screw is located here at the top of the throttle body, facing towards the firewall.
Remove the old O ring. You may need to cut it. Clean up the idle screw whilst it's out of the engine.
Push the new O ring in position. I used a little bit of oil to help.
Replace the screw returning it to it's old position. Turn on the car and adjust idle speed. Check with both electrics (lights and aircon) on and off. Typical idle speeds are around 900 rpm.

First published: 25/03/19
Last updated: 27/02/23

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