02 Impreza OBS that is having some interesting intermittent issues. Automatic with about 75,000 miles

 

Symptoms

 

Under acceleration the car lacks power and acts like its going to die.

 

Shifts erratically. When you accelerate a little it will drop a gear and nearly redline, and sometimes it won't down shift when it should and bog down.

 

Seems to make a slight popping sound, sort of like popcorn.

 

It has an intermittent CEL, I haven't been able to pull a code from it because it doesn't usually come on and its my friends car.

 

I was thinking some sort of faulty sensor?

Any ideas?

Pull the codes.

 

A tuneup is over due (plugs wires filters pcv valve)

The popping sounds can be ping, which woudl indicate a non responsive knock sensor.

 

Lets start with a full tuneup first

 

for giggles when was the timing belt replaced last