ok ive got a 05 impreza has 2.5sohc engine ive been losing power lately hills i use to climb in 5th im now barely holding 4th and even sometimes down in 3rd the car is using about a qt. of oil every 150 to 200 miles no signs of leaks ive looked all over the engine and its not blowing smoke have no clue where its going, and its pinging boarder line knocking mainly on the highway with little to no load if i put more load on it it goes away, ive replaced the plugs and have checked them since looks like its running a little on the lean side but not too bad. it will throw a cel for the vapor recovery same code if you have a loose gas cap and cruise light will start flashing but no knock sensor codes or anything like that. if any one has any suggestions or ideas im all ears ive been scratching my head since december on this

Edited May 9, 20169 yr by yosyeti

maybe more than one item but, despite no code, symptoms kinda point to knock sensor. If it looks cracked - it isn't hard or expensive to replace. almost the only sensor than doesn't need to be OEM - cheap ebay units have worked well for most people.

 

could your clutch be slipping?

 

PCV valve may also be gummed-up.

it had a new clutch and pcv put in it right around 20,000mi ago when had the engine rebuilt ill try a knock sensor next pay check i dont believe it was replaced when the engine was rebuilt. with the knock sensor i know it changes the timing to keep it from pinging but will it also change the amount of fuel to cause it to run lean.

Edited May 9, 20169 yr by yosyeti

does it idle normally?

idles smooth sounds good till it starts pinging around 2350rpm under light load conditions and come to think of it i only ever hear it ping in 4th and 5th, and it just lacks power 

clogged Catalytic Converter?