Hey everyone.

I've been doing a lot of work to my newly acquired 1998 Legacy Outback EJ25D. I've straightened out a lot of issues I've been having with it, but one still remains.

192,000 miles on the car, unknown mileage on engine (replaced at one point in time)
 

If the car cools completely down, like in the mornings, I'll crank it up-will start and run fine, but when I start driving it-the car has an obvious hesitation problem. Usually in light to mid throttle. Doesn't feel like a misfire, just feels like all the power is gone. Once it gets up in to the higher RPMs it takes off.

 

About 10 minutes of driving and it's running just fine. The weather is pretty warm here in Georgia so the symptoms are pretty much for morning starts. Its fine for the rest of the day.

Recent repairs include:

New Knock Sensor (Took care of the P0325 code)

Used MAF-helped a lot after installing, car would actually sputter and die with the old one

Used Fuel Pump-this was due to an extended cranking issue-fuel pressure is at a pretty steady 32 PSI
EGR System repair - P0400 code, replaced vacuum solenoid and vacuum modulator.
Set of plugs, factory NGK (maintenance)
Timing belt & accessories (maintenance)
Fuel filter (maintenance)
Transmission service (maintenance)

If anyone has any pointers that may help me, it would be greatly appreciated. I may start looking towards the coolant temp sensor, I'll put my scan tool on it and monitor the data.

Seems I remember that the coolant temp sensor sends a signal to the computer to make the fuel mix richer until the engine warms up. Yea, good guess that the coolant temp sensor is the problem.

Consider new plug wires.  Get OEM or NGK--do not use parts store cheapies!

Thanks for the help. I'll let the car cool down completely and monitor what the coolant temp data says.

 

I found a set of nearly new Napa Belden wires on a 1998 Outback at the junkyard, still shiny and new, I grabbed them. I have a set of Belden wires on my 99 Neon and they have almost 70,000 miles on them.

 

However, I have the older style ignition coil on my car-since whoever replaced the engine years ago used a 1996-1997 engine/harness. I'll probably upgrade to a newer style coil, unless if the older style ones are more robust.

Update 6/3/15

The car has been performing well. I have yet to do the plug wires and coil, but that's back burner. I was chasing an electrical issue with my temperature gauge, I cleaned off all the engine and engine compartment grounds, since then the battlewagon has been working well. The temperature gauge still has issues-that's for another topic.

Another theory:

My car did (and does) the same thing with both motors, first the EJ25D and now the EJ22E. New motor had new ignition everything but coil.

Apparently the ECM runs the motors super rich (until high RPM- emergency accel sort of thing) just to help the motor. No motor likes the cold run normally, and being hard on them is worse. Not saying its bad to drive them cold, but thermal expansion combined with metal parts winging around inside a big metal part isnt really great for any of those metal parts involved.