timing, set for mark or for pep?

[TominMO]

theoretically what you did should not make any difference. once the O2 sensor warms up and starts sending a signal to the computer, the computer takes over advancing the timing to minimize the unburnt fuel in the exhaust. when you manually set the timing you are setting the "base" timing". when the engine is cold the distributor in my older '89 model has both vacuum and centrifugal timing advance but when the O2 sensor gets going the computer overrides that and advances the timing itself. the override is done in the ICM (ignition control module) circuits.

Here is a thread I started over on the Subaru board to ask people much more knowledgeable than me about this. I found it helpful.

http://www.ultimatesubaru.org/forum/showthread.php?t=78559

[hihobmw]

A automobile runs in closed loop mode generally only at an idle, and at a constant speed on near level ground. If you are pulling a hill, or accelerating at all, it probably is not in the closed loop mode.