I am using my car since 2009, i bought it as unused, new (2009 mcs, now it's at 65k km, still stock). And I was driving it at 5.9l-6.5l/100km till last 2 months.

I was abroad, so my dad used my car for about 3-4 days. That's when everything is changed. Now my car burning almost 10l/100km under same conditions. And my main concern is, when you're driving 2k-3k rpm, and let's say, going downhill without pushing accel. pedal, there is a "huvm huvm huvm" sound coming from the engine. it does this sound if you press accelerator too but it's more obvious without any load.

Now i bought new spark plugs and air filter, they're shipping now. they probably change things a bit but, this humming sound...

I also tried to video this, but here in Turkey, there is no flawless tarmac anywhere, so all you hear is squeals and plasticy sounds coming from the cabin.

Any ideas? HPFP? Carbon Buildup? Exhaust or Exhaust Manifold?

--ohh, it's not about fuel, i am driving on shell fuelsave 95 since i came back, 1.5 months ago. i drove almost 3k km, and nothing has changed.

 

Does the noise change pitch or loudness with RPM? With road speed?

If it is associated with road speed and independent of engine RPM, the problem is most likely something like a dragging brake or bad wheel bearing or some such. If the noise changes with engine RPM, independent of road speed, then it is most likely something to do with the engine.

 

yes, i thought it could be from tires or brakes too, because brakes has to be changed, but no. it is not related with speed. it's definitely from engine.