Diesels don't follow the same rules as a gas car for lean = high egts and melting cylinders. Too much fuel is what causes melt down. The air intake is totally open, engine output and rpm is solely dependant on fueling. At idle, the air/fuel ratio is something above 100:1.
I'm not saying you wont be able to spin the turbo, but the idea behind the AFC housing is to be a smoke limiter. The injection pump at a given full load screw setting will be able to pump out X amount of fuel. With the AFC housing connected, when off boost you will get less than that amount even at full throttle. Full fueling potential wont happen untill boost is there. The idea is to give more fuel to go with the extra boost. Does some go out the exhaust, yes, but if you have the AFC housing set properly it wont. The eco diesel was a marketing thing with VW. I have never heard of one getting significantly more mileage than a regular 1.6TD.
As I said combined mileage may get better because when accelerating you will never get the extra fuel the afc housing provides, but at constant speed, the fuel needed to push the car at 70mph is a given amount. Whether or not the afc housing is connected wont make a difference. If the spring was set too soft and it was actually injecting more fuel than it should at say 3 or 4lbs of boost, that just means to maintain your same speed you will just back off the throttle a bit.
Jason
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