-2017 Hyundai Accent 1.6L GDI
-~176,000 Km
-engine swap at ~168,000 Km
-new engine has ~50,000 Km
-Old engine was a bent rod (allegedly)
Old engine had Cold Air installed, for the new engine I immediately replaced the factory airbox, in case that was my problem.
-new Catalytic Converter (aftermarket) installed at the same time as engine swap and has seen ~8000km of drive time.

Hey Enthusiasts! First time posting and I’ve got a head scratcher for you.

My 2017 Hyundai Accent is having trouble regulating the idle speed, there is also minor power loss at low rpm’s, which I don’t really notice at higher rpm. Also p0420 code (but new cat installed recently) so my local grease monkey fooled the computer into ignoring the cat for now.

There is also a very slow oil leak at the crankshaft. It took a week of cleaning and driving to finally establish the source. That will be fixed quite soon. Due to the high velocity spray, my engine compartment gets pretty messy, pretty quick but it doesn’t seem to leak at all at idle. Techs kept it running on the hoist for nearly 3 hours and not a single drop was detected.

I’ve pulled all the plugs and they look fine to me. Oil is not getting into the well. Insulation is browned at the base of the insulation but it’s extremely light and I had to squint to really see it. Wear appears even on all 4 plugs and the internal part of the plugs are still nice and shiny and mostly new looking. Intake box is brand new with a brand new looking filter even after driving ~8000Km. 1 wire recently replaced in response to a p0302.

Scenario 1

Sometimes I’ll sit idling in my car for hours. Covid has not been nice to our little company so I’m always at the ready, but not usually moving.

Periodically and seemingly randomly my rpm will go up and down. It’s almost always down, and when it drops down it stays there for a while sometimes coming back up to normal briefly before falling back down. Normal seems to be about 750rpm and when it drops it seems to be bouncing around at 550-600. I also notice this more frequently when idling in drive at a stoplight.

Scenario 2

After a few minutes of highway driving (usually a bit above the limit) getting off the highway is cause for concern. Sometimes when I finish coming to a stop at the end of the ramp the rpm will sink down even lower and the car will shake… not violently… but enough to make me worried it might stall. The faster I stop, the more aggressive the shake.

Im not a mechanical fellow, but I’m struggling to trust the shops around here now (story for another day). I have some basic tools and a couple bucks to pickup a couple other basic tools but my garage is in no way equipped for mechanical repairs.

In case it matters.

- All power features work fine
- cruise control experiences the same issues I do
- have done a manual relearn of Throttle position
- A/C / Heater working fine
- recently changed the oil
- power seems better when I use the manual shift mode. Could easily be attributed to driver manipulation though as I allow rpm to be a bit higher between shifts when shifting myself.
- serpentine belt recently replaced because the oil mess destroyed the previous one
- I’ve never noticed an issue when running cold from a fresh start. Issues arise when the engine reaches temp.

Dont be shy to ask questions. If special diagnostics tools are required, I can’t likely run the test for you. Again I do have a couple bucks to grab a tool or two, but nothing too pricey. <$100CAD.

***EDIT***

I have access to a reasonable scan tool, I just don’t know how to read the data streams, or what the optimal readings should be for those streams. It shows me a Min threshold, and a Max threshold for many many sensors, as well as being able to represent the readings as graphs, percentages, and plain text. It’s a FIXD Auto Bluetooth ODBII Scanner, and transmits to their App on my iPhone. I literally JUST pulled it out of the mailbox. Hence the Edit.