[Blacktree]

I have an '02 Jetta TDI, with the 5-speed manual gearbox. I bought it in 2015, and drove it daily until last month. The car is mostly stock, with all the emissions equipment still intact.

When I bought the car, the intake manifold was caked with carbon deposits. It's a common thing with these engines. Soot from the EGR mixes with oil vapors from the PCV system to make black sludge in the intake manifold. I was told that driving more aggressively can mitigate it. So I learned to accelerate briskly up to cruising speed. I also added a catch can, to reduce the oil vapors going into the intake.

Diesel engines also use very little fuel during idle. So if you can get up to cruising speed quickly, then start using P&G, the car should reward you with good fuel economy.

That said, I don't rev the engine very high. The engine's torque curve is similar to the boost curve posted on page 1. So going past 3000 RPM (on a stock engine) is basically pointless. When accelerating, I prefer to upshift around 2500-2700 RPM, which puts the engine at peak torque in the next gear.

I have to admit, I get lazy when it comes to hypermiling. But I try get up to cruising speed quickly. Plus I get off the throttle and disengage the clutch as much as possible. With this half-hearted hypermiling, the car averaged over 40 mpg. I'm sure you could do better.

I should also add that on a modified engine, the situation could be totally different. It would depend on the nature of the mods, and the tune. For example, with an EGR delete and a catch can, you don't need to worry about the intake clogging anymore. And a custom tune will shift the torque peak higher in the RPM range.