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There is a mixture screw at the base of the carburettor, this is the fuel mixture screw for idle.
On a pre emission carburettor you wind it out to add fuel.
On a emission carburetor you wind it out to add air to lean mixture.

On a emission carburetor the mixture screw may be hidden behind a plug to prevent tampering and which was to prevent people changing the vehicle emissions.

I don't know when the change is mixture screw setting came into effect, you will have to use your initiative here.

All I really want is you adjust until you have a nice steady idle at the specified rev's before we go on with the diagnoses.

When you fit the new PCV, you will need to reset this.