ADDITIONAL SYSTEMS THAT CAN GO WRONG

1 Idle solenoid

An electric solenoid valve blocks the idle fuel jet to prevent running-on. It’s switched through the car’s ignition. The car won’t idle if it’s broken or if it’s not getting power due to dodgy wiring, or similar.

2 Bypass idle systems

Recognisable by a large remote idle speed (or ‘volume’) screw. The throttle should be set fully closed at idle. Susceptible to dirt and air ingress. Check the adjusting screws’ sealing O-rings.

3 Disc valve chokes

A disc valve choke is like a miniature carburettor in its own right, with a tiny reservoir for initial starting and fuel-air metering for when that’s exhausted. The disc is sprung against the body.