Rough startup, twice

[PalmettoPrecision]

I experienced something twice today that has never happened with my ‘21. Car is bone stock.

I parked the car on a flat surface to walk into a store for about 20-30 minutes. Upon returning I started the car as I normally would and experienced what I can best describe as a “rough start” with relatively significant vibrations through the seat and floor. It surprised me, so I shut it down. Restarted with no issues. About two hours later after leaving a different location I started the car and experienced the same thing - rough, vibrating startup that didn’t sound particularly abnormal but sure felt abnormally “rough”.

The vehicle was already at operating temp both times. Car was in sport mode during the start. Both times felt almost identical in terms of severity/shaking. Car seems to run and drive normal - no hesitation with throttle, no CEL, full power, clean idle. Even hit WOT on the way home and it felt great as always.

Any ideas on what could be going on?

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[Mason]

How is the car starting in sport mode?

 

[PalmettoPrecision]

How is the car starting in sport mode?

Sport button, start button.

 

[zrk]

How is the car starting in sport mode?

Also, you can bimmercode in the mode that you want to start in.

 

[3TMagnetMan]

Is it rough idle and shuddering and shaking???? Bad Gas???

 

[PalmettoPrecision]

Is it rough idle and shuddering and shaking???? Bad Gas???

No rough idle. Other driving characteristics have been fine. Very odd. Have not been able to replicate.

 

[Late-Apex]

I've encountered the same issue intermittently on warm starts. Doesn't seem to effect anything and it happens so rarely I haven't bothered wasting my time at the stealership.

 

[STV3]

I think I've been feeling something similar recently. Almost feels like a jolt going through the car as it starts. Happens randomly.

 

[Joey MKV]

Anyone find the culprit to this? I've been getting rough starts, normally this first start of the day then after that starts up and runs perfect. It's just that first start of the day. It almost feels as if its not going to start for a second before actually firing. I thought maybe it was my battery being low and not getting charged up since i dont do a lot of distance driving. I hooked it up to a ctek battery tender yesterday, showed low left it charging until full. This morning same rough start up. Anyone got an idea?

 

[zrk]

Bad fuel, or ethanol. Ethanol often starts real hard.

 

[Juan115]

I usually get this too. Feels like it’s going to turn on. I have a short drive to work and sometimes temps don’t get up to what they’re supposed to. Wonder if this is why.

 

[MoralxSupport]

Bad fuel, or ethanol. Ethanol often starts real hard.

Yeap, came to say this. I notice a difference when running ethanol. Never had it happen when the car was stock.

 

[PearlSup]

If I don’t drive mine for more than 24 hours (rare), the next cold start always seemed to be kind of “meh”. I attributed this to a lazy/undercharged battery.

I also noticed that the car would “shudder” a little while idling at the first stop light of the day. Experienced this on my 2018 86 as well.

Really odd is I haven’t had either issue since I installed my single-exit Tomei. Maybe better exhaust flow helped both these issues?

 

[Mason]

My car starts rough since I got it tuned. I assume it’s normal..

If it starts and settles down then I wouldn’t really worry imo

 

[Joey MKV]

My car starts rough since I got it tuned. I assume it’s normal..

If it starts and settles down then I wouldn’t really worry imo

I hope so. Mine did it stock here and there but now daily on a cold start she struggles to turn on for sec. Just doesn't seem to be normal to me. Especially since I only have 1.5k miles on the car

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