1980 lambda-CIS: Coast or go to neutral?

[bsimonson]

Hi,

I have a fairly good understanding of the lambda-CIS on my '80 US-spec SC, however I can't make up my mind if it's better to coast or go to neutral when going downhill (if fuel-saving is the priority).

Assumption #1 – Coasting is better:

• For: Since the engine is being run by the wheels it will consume less fuel due to system sensing there is no throttle input and using the freq.valve to down-adjust the fuel-flow.
• Against: The system is not clever enough (as more modern systems are) to sense the above and the increased revs of the engine will draw the fuel-meter plate up resulting in more fuel being injected.

Assumption #2 – Neutral is better:

• For: The closed throttle plate will limit the lift of the fuel-meter plate thus giving the same amount of fuel injected as when idling and you get the benefit of keeping the speed up due to lack of engine braking.
• Against: The engine needs to consume fuel to keep going at idle instead of being ran by the momentum of the car.

Anyone care to enlighten me what is correct? I also realise that the benefits are small so this is more out of curiosity than anything else.

Cheers!