i had been meaning to ask someone about this, i noticed after babying my lude for a little while, then driving it more aggressively it seems to run a lot better smoother and whatnot, even better mileage (actually it might be worse mileage, one or the other, but noticable none the less) i thought that was the reason, the higher pressure and what not cleaned things out, thanks for clearing that uptry replacing the spark plugs. if the plugs are old and worn out, they may have developed some hot spots that are acting like glow plugs.
or it may just have a crapload of carbon buildup, in which case you'd want to run a can of seafoam through a vacuum line while holding it at about 2k in neutral.
or, if you think its up to the task, just go and drive the ever living snot out of it for a bit, as long as the engine is in good enough shape to handle the load, the romping actually does wonders for cleaning things out, seriously. babying a car for too long can cause excessive buildup inside the combustion chambers. driving it hard heats it up and burns it off, and the high revs have higher air velocities which literally blows the stuff right out after it starts burning up the buildup