Harsh start after a few days without engine use

This is only a guess, but my first thought is that it's oil pressure related. When an engine stops, there are check valves to prevent all the oil from falling back into the oil pan. That means there's effectively full oil pressure immediately on the next start. But no system like this is perfect, so if you let the engine go long enough between starts, the oil will manage to leak past/through the check valves and the engine won't have full oil for those first tenths of a second on that next start.

There will still be a film of oil on all surfaces, so excessive wear shouldn't be a major issue, but it will take that bit of time to refill all the oil galleys and get up to full pressure. Also, the variable valve timing on the exhaust camshaft is controlled by oil pressure, so maybe that's contributing to that first half second of engine roughness.

Hopefully other PHEV owners can say whether this is typical behavior or abnormal. I'm leaning towards typical, but I'm a HEV owner and can't recreate the issue reliably.

The other thought that comes to mind is rust related, but I really really doubt that's the case.



Honestly, I'd try to make sure to run the ICE about once a week for 15 minutes or so. It's just best practice to keep everything well-lubricated and to get the oil temp up high enough to burn off any water or gas contamination. This is doubly true in winter(the M20A and A25A engines have known issues with moisture buildup in the oil(from condensation) when they're not allowed to get to full temp in winter). It's also a bit helpful to not let gas just sit in the fuel injection system for weeks at a time. Not a big big deal, but flushing newer fuel through the system every week or so decreases the likelihood of a problem down the road.



Now I'm just some internet hack, so absolutely do not take my thoughts as gospel. But I am repeating the once a week advice from someone with over a decade of working on tens of thousands of Toyotas and Lexuses.

 

You typically let the car run through the battery capacity, on weekdays? Then on the weekends, the same, and the engine just kicks in due to longer trips, depleted charge? Or you purposely start the car like a regular hybrid?

 

[removed]

 

Yes, I've noticed my engine sounding a bit different when she starts up after sitting for a while....I don't like it, either!! But she's going on 70,000 and the oil still looks pretty clean after 5,000 miles so that's a good sign.

Because I take my Prius to work (a 40-mile commute) I don't like the idea of the engine having to run hard right away so I've learned that, when I turn on the car in the garage, if I tap the gas pedal a little it will cause the gas engine to come on....I like to get it a little warm before going 60 mph on her.

 

You can experience "harsh starts" depending on how deep your on the gas pedal during transitions from EV to HV. I prefer to regulate mine and manually switch over to HV; once I'm on the highway, up to traffic speed and off the pedal. My transitions are quiet smooth, but this is also a gen4 with only a 25 mile EV range. Once the engine is warmed up for the first time; I only notice the transitions through pedal feel and slight lost of power; in ECO mode. I understand that if you keep your car in normal or sports mode, you would feel less power loss and a more responsive pedal; at the cost of lower mpg.

Good Luck.....