Engine stuttering

[HHR_tune]

For the last couple of days, I have been getting random engine stuttering (Chevy HHR 2008 LT 2.4 manual, 100'000 miles). When this issue occurs, stepping on the throttle sometimes doesn't seem to trigger a response and then one or two seconds later, the engine responds, but sluggishly. The car then feels as if it had no power.

CEL light doesn't light up, but I sometimes get these two engine codes:
P171: System too lean
P300: cylinder misfire

When stepping out of the car after the stuttering has occured, there is quite a pronounced fuel smell (not gasoline smell per se, but the kind of smell you get with bad combustion).

In the attached log file, the stuttering starts at about 08:24 until the end of the log. Is there anything in the log which could indicate the cause of the stuttering?2224.Channels.xml2224.Layout.xmlstutter.hpl

[TheMechanic]

Do your diagnostic. You have codes. Check them out. Could have a fuel pump failing given you have a P0171 and P0300. Could be a bad coil/plug. When was it tuned up last. Don't start with tune issues until you have mechanical issues solved.
Freeze Frame data is your friend.