Vacuum gauge instead of Scangauge?

[Telco]

On the vacuum gauge, it works more for a carbed vehicle than a fuel injected one. A carb uses airflow across a venturi to create a vacuum at a specific point to mix fuel into the air, but under a situation where the carb is in a full vacuum condition doe to the throttle plate being closed it won't draw as much. On a fuel injected vehicle, the engine is going to put in fuel depending on the O2 sensor in closed loop, with input from the TPS, MAF and IAT with the primary reading coming from the O2. Keeping it in a high vacuum state doesn't make that much difference on fuel injection, at least it didn't when I tried it a few years ago. Pre-computer cars with engine economy gauges were just vacuum gauges.

On the P&G with slight throttle, I think there is something to that. I don't do P&G after trying it and seeing my mileage drop (my engine is too underpowered for the vehicle, takes way too much gas and time to get the speed back up) but I have noticed that if I have a very slight throttle on I can coast farther than I can with no throttle. I figure that with the throttle slightly open, the engine isn't trying to draw air from the tiny idle bleed hole, it's getting it from a much larger area so it isn't pulling nearly as hard.