1996 Hyundai Accent Hyundai Accent high oil usage/ engine '

Hi all! This is a great forum would like to donate but not sure how I have no credit card.

I purchased a 2nd hand Hyundai Accent 1.5 1996 model about a month ago. When I purchased it only real problem I could hear was hole in the 'box' of the exhaust.

I have since had the exhaust fixed, and the car serviced, all was fine except for a really dirty air filter. Since the service the car has the following symptoms:
Starts fine every time
Idling is uneven and not as good as it was when I purchased it.
The car requires about 2 liters of oil a month otherwise it runs too low.
Recently, there has been a 'sucking' noise sound from the engine. The car loses power (when driving about 20km) every now and again, it feels as if it's going to cut out (but hasn't yet)

I was advised to change spark plug wires, which I have, but problem still exists. I fear there may be something dirty inside the engine/ or insiide the fuel injectors. I have heard 'seafoam' is an option but haven't yet tried that.

Your help would be greatly appreciated

Thanks, Carl