Ok, hopefully someone will have an idea what might be going on here. I've got a 94 EJ18 impreza. If I'm at near full throttle, pulling up through the power band, say like I'm accelerating in 2nd gear, the engine bogs and seems like it's pulling at 80%. Then, at around 2500-3000 RPM I hear a single audible 'click' like that of a relay, and the engine comes alive and starts pulling noticeably harder. This happens very frequently and has been since I bought the car 30k miles ago. Not a big deal, I'm just wondering what might be causing this.

 

I didn't realize my lowly ej18 had vtec, lol. I kid, I kid.

AC on?

 

When was the last time it had a tune-up?

it's had spark plugs, air filter, all belts, timing belt, valve cover gaskets changed when I got it 25k miles ago. It's not that it's running badly, it's not. It's that there's a noticeable transition in throttle response caused by SOMETHING, but I just want to know what it might be. EGR valve?

Does the A/C compressor clutch engage even if the heat/fan blower is on, but not the A/C? I know on my 2005 impreza it does, but I didn't think it did on the 1994.

It comes on with the defrost settings. That's about the only thing I know of that would literally "click" and instantly make a difference in engine power.

 

Unless your click isn't a click, but a knock instead. Maybe check your knock sensor for cracks.

Ah that's probably it, I usually have my heater control set to mix defrost/floor or to defrost. I didn't know it caused A/C to kick on... Is this really true?

Yes its true.

if elmo says it's true, it must be true.