2001 Subaru Legacy L: Bucks after starting, sometimes, but if so continues bucking until stop then start engine again.

[jmo]

Intermittent problem with bucking. It either bucks from the time I start it, or it doesn't buck. It is as if the computer is reading something incorrectly on startup and then using that bad information until the next start. I do not know what info that would be. No engine light except during the extreme bucking, and then it clears. So no engine light afterwards, and I assume no code. (will check that). Is it possible for the crank position sensor to be bad but not throw a code?

 

[bmart]

Does bucks from starting mean without it in gear? Without it moving? Only when it is moving. Always when it is moving?

Bad fuel would be #1 cause. American fuel is pretty crappy and many times has water in it. Water is heavier than fuel, so the pump pumps it first.

 

[manicmechanic007]

Slow to build fuel pressure?
Cycle the key on a few times before you try to start it next time
Check the fuel pressure
Intake valve deposits require long crank times when everything else is fine
That carbon on the intake valves acts like a sponge, and sucks up a bunch of gas before letting any into the chambers
Just a thought
Check those plug wires at night, look for lightning at the boots, spray them with a squirt bottle of water, see if they break down