IT may be from a small leak in the fittings for the fuel lines.
These engines are GDI - Direct Inject - meaning they have a very high pressure fuel line going to the engine.
That pressure is needed to allow the fuel to spray into the cylinder during a compression stroke. Near the top portion of the stroke - so it really needs a high pressure to spray into that air charge as it can be compressed above several atmospheres of pressure (roughly 15psi at sea level) - these 3-cylinder thingys have turbos on them else being a typical 3-cylinder and if it was Naturally Aspirated (no turbo) you'd have a few problems trying to get these things up to highway merge ramp speeds - you'd run out of ramp before you could safely merge at their (highway) speeds. (READ: Slow - See Chevy Sprint)
The TDi - VVT ones (like the Sigma 4-cylinder N/A Normally Aspirated) types still spray fuel that is at a high pressure - just not as high pressurized system the GDI systems are, and is vacuumed in, during the Intake stroke, so the fuel is pulled into the cylinder in a vacuum-condition as the cylinder fills up with air and fuel. Then the compression stroke occurs and the plugs fire at the right time determined by their sensors and systems so it can produce power.
So take it to a mechanic and check your reassembly efforts - make sure you have everything clamped and fastened down and the outside air intake cowl is sealed properly so your not sucking in engine fumes when the heaters are on.