Engine dropping below idle, stutters, comes back up to idle.

[chocstraw]

Occasionally, maybe once every 3-4 days, I'll be sitting in traffic or at a red light, and my engine will dip down to 300ish RPM then sputter and come back up to idle.

Battery is new, plugs have 10k on them, gas is CA 91. 84k miles.

No codes thrown, I'm thinking it might be fuel pump or ignition coil. Any idea where to check and how to get this fixed on warranty without codes or a readily repeatable issue?

[J-aec]

I have the same issue as well. Albeit a Minor one. Just curious as to what it might be.

[drrust]

Does it occur just after a fill up? If so replace the fuel tank breather valve. The is a DIY.

[thehounder]

If it's right after a fill-up its definitely the breather... Do you ever get "tighten gas cap" warnings?

[bvrider1]

Hey OP, do you have an aftermarket tune?

[wfdeacon88]

First thing to check is the easiest... the gas cap..even if the sensor isn't tripped saying "tighten gas cap" it could be worn out or not sealed. Mine would click, but when I went to open it later, it would just be sitting there loosely. (green one is my original, left side is my new OEM cap from FCP euro). The new one actually locks and isn't moving.

If that doesn't work, it might be your fuel breather valve, which is cheap. I haven't changed mine yet, but if my idle thing comes back (exactly what you experienced), that will be what I do next.

[chocstraw]

Originally Posted by wfdeacon88

First thing to check is the easiest... the gas cap..even if the sensor isn't tripped saying "tighten gas cap" it could be worn out or not sealed. Mine would click, but when I went to open it later, it would just be sitting there loosely. (green one is my original, left side is my new OEM cap from FCP euro). The new one actually locks and isn't moving.

If that doesn't work, it might be your fuel breather valve, which is cheap. I haven't changed mine yet, but if my idle thing comes back (exactly what you experienced), that will be what I do next.

These new caps feel so much cheaper, much lower quality but I suppose the seal is just the same. The green one has a much better heft to it. It has been a few days since I've gotten gas or had this happen. I'll see if it happens after my next fill up.

Any codes to look out for?

[drrust]

When my breather valve went, there were no codes. I would get some rough idle and stalling just after a fill up.

[wfdeacon88]

Originally Posted by chocstraw

These new caps feel so much cheaper, much lower quality but I suppose the seal is just the same. The green one has a much better heft to it. It has been a few days since I've gotten gas or had this happen. I'll see if it happens after my next fill up.

Any codes to look out for?

So agreed, the weight of the green one is more... however, the difference in seal on the new one is crazy good comparably. the green cap just clicked, but never actually locks in... plus, if it's old, the gaskets are probably shot... my sensor never detected the gas cap being loose, but when I went to fill up, it always felt loose despite the click. The new OEM one I got literally locks into place.. like you feel it snap and close. Since doing this, I haven't had a rough idle.. fingers crossed. Definitely having that snug fit is better for the system (I think!).

[Richbot]

Good fit keeps from overworking the evap system too

Good to hear that can be a cause of this - my car is 11 years old now and I happen to have a spare unused cap from a box o'parts I bought from somebody's racecar teardown. Mine was doing it very very infrequently after long highway drives, in the cooler weather this spring and it went away.

[wfdeacon88]

Originally Posted by Richbot

Good fit keeps from overworking the evap system too

Good to hear that can be a cause of this - my car is 11 years old now and I happen to have a spare unused cap from a box o'parts I bought from somebody's racecar teardown. Mine was doing it very very infrequently after long highway drives, in the cooler weather this spring and it went away.

Agreed, dead on when mine does/did it... it was oddly consistent.. on my drive home, which is 26 miles, I would get to the same exact stoplight off the highway (only in the afternoon when temps are hot) and coming to a stop, boom... a second or three of slight bouncing exactly as OP described. Normally, in the summer temps at the same stop light every time. the Gas cap might have helped, but I'm not mechanically knowledgeable so maybe that's a fluke... definitely after driving highway and definitely more in hot weather. Does this mean it can be pinpointed as something specific?