I have a 1999 legacy 2.2 that is sluggish, lacks power and sputters until it reaches about 3300 RPM's, then it's like something kicks in and the cars runs great. If the car is allowed to cool off and you reset the ECU (Unplug the ECU or battery) the issue temperately goes away, but after running for approximately 20 - 30 minutes, the issue slowly returns. Any idea's?

Is the check engine light on? If it is I would start by checking the codes.

 

I suggest that you don't drive it like this, because you might be damaging the cattilitic converter.

Nope, I don't have a check engine light on. I even scanned it to make sure there weren't any soft codes. 

Okay, does it smell like its running rich, can you smell fuel when its doing this?

I've actually hooked up a monitor and it's running lean when it's not running well. 

Okay, I would start by checking for a vaccume leak, I would start by checking the IACV it could be stick open. Maybe check for disconnected hoses first.

I have a 1999 legacy 2.2 that is sluggish, lacks power and sputters until it reaches about 3300 RPM's, then it's like something kicks in and the cars runs great. If the car is allowed to cool off and you reset the ECU (Unplug the ECU or battery) the issue temperately goes away, but after running for approximately 20 - 30 minutes, the issue slowly returns. Any idea's?

 

Install new plug wires, and put a can of techron (or other injector cleaner) in the gas tank when it's <1/4 full.

 

Heat may also be affecting your coilpack, but do the other stuff before you start to diagnose that.

Hm just taking a random shot, there have been people who have posted about strange issues that did not throw a code which turned out to be the front o2 sensor. I wonder if maybe when it's in closed loop is when it has no power until 3300 rpm? I don't know the details maybe it goes into open loop above that rpm or something? Because how you mention it works for maybe 20 minutes after unhooking the battery seems like it is something it is learning improperly. Also if your scanner will show the engine coolant temp does it seem reasonable?

I just bought a new front O2 sensor for my 99 outback a month ago for $50 and its was OEM bosch. I beleive I found it on partsgeek.com worked great for me.

You might have a dirty contacts throttle position sensor.