Well how many things can cause that.
1 Not enough fuel.
2 Not enough air.
3 Bad ignition timing i think would do it.
A bad sensor or something could cause a bad fuel mix.
If it's cold where you are i would try taking the air flow meter of and see if it's still moving freely, and check for any ice that may have formed over the winter. Especially if your air filter sits under the vent like on most MK1's. (i don't know where the 3sgte one usually is
) So i guess take the air filter off any if you thing it's clogged with ice warm it up inside. I'm not sure if they can actually ice up enough to do that, but i've had snow clog mine up pretty bad sometimes.
The engine runs smoothly though?
I've hear lots of people who've had their AFM get clogged right up with ice to the point where they had to bring in inside to melt enough to use.
I've never taken mine off to check, but quite a few times i'm pretty sure i've had it stick, because i felt the engine sputtering pretty bad, and had to rev a bit.