I’ve had my car for 12 years now (Hyundai accent), and whenever it’s due for service the spark plugs start misfiring. So after a service and new plugs are put in, the car runs fine.

But building up to the recent service it had, the car was chowing oil like crazy yet there was no leaks and no smoke coming out the exhaust, and it felt like the spark plug were misfiring again.

After the service the car was fine, but the next day on a road trip it had no guts. Drove 776km (485mi) and my oil was empty again. Oil was topped up and no issues there since, but mentioning it in case its relevant.

My issue now is my acceleration is “meh”, and on an uphill I can sit in 2nd gear around 5000rpm, and the car STRUGGLES to even maintain 40km/h (25mph). I decided to check for myself if the spark plugs were in fact replaced, and they looked to be fine.

I raised this with my mechanic and he advised it could be related to the oil issue, and if the service didn’t fix the issue, then he’ll have to strip the entire engine, which I cannot afford.

So before I spend another cent getting this looked at, what could be the reason my car has no guts going uphill and why the power has suddenly plummeted? I just want to get an idea of my options before agreeing to extreme measures to fix