This miss has me stumped

Does this happen when you idle? How many miles on the car?

SM-N900P ?

 

Need to check for vacuum leaks, exhaust leaks, check/clean MAF sensor, clean throttle, and check/replace spark plugs. It could be bad electric connections and dying coil, too. Am I forgetting something else?.

One more thing, plugged EGR pipes.

 

I would hook up a bluetooth obdII tool and use the torque app and takes some logs. If any of your sensors are dropping out, that's likely your culprit. Check wiring for bad connectors, or pinched wiring etc...

Was it a plug and play A/F sensor, or did you have to splice the wires?

 

Maybe remove and check the plugs? 1000 miles ago is quite recent.

SM-N900P ?

 

What plugs did you use?

Not always, depending on severity of the issue.

 

Scanguage II is nice, but it doesn't do what the TOrque app does. I have a $13 bluetooth adapter i bought on amazon, and the torque app on my phone is $5. So for $18 total, you have an incredibly powerful diagnostic tool.

You need to log and graph all the parameters. If you take a log and post it, perhaps we can all help analyze it for you to see what's dipping out and potential causes. It's hard to diagnose intermittant problems without putting it up on a graph.

Also, spark plugs could cause this problem too. You might have gotten a bum one. Are they NGK? Check those and the wires. I normally replace the spark plug wires with a spark plug change because resisitance in the wire will build over time, and even a small increase will lower the voltage and current seen at the spark plug tip. Now 90k miles, the wires should still function just fine, i just do it because i'm anal about making sure everything is optimal.

Check this answer:
Will spark plugs and wiring cause the car to cut off while driving

 

Modern cars have the coil-on-plug technology, hence no HV wires.

 

Oh yea, i forgot. Either way, i would normally still replace them when i do plugs. It's just much saltier at $200 for a set of 4 coil/wires.

 

Did you end up getting your problem fixed?

I'd check to make sure the spark plugs are properly gapped. Even pre gapped plugs sometimes are a bit off. Id also check to make sure the coil on plugs are properly seated, and that the spark plugs are torqued properly.

 

If the gap is close to spec I'd leave them alone, they're fragile and manufacturers caution about re-gapping: it's not impossible, but should be done with extreme care, and only if really necessary:

Frequently Asked Questions: DENSO Iridium

 

Have you solved this yet? If not, it sounds like you may have a weak ignition coil, which is difficult to diagnose until it gets bad enough to set a code. A weak coil will cause a miss in lean fuel conditions like you describe, but will disappear when you step on the accelerator and give it more gas. You could buy one new coil and substitute it for the existing coils until the miss goes away or you could wait for a code which will tell you which coil is bad. Other less likely possibilities are defective power or signal wires to the coil(s). Good luck.

 

Was it solved? My 2010 Prius has had a gradually increasing misfire that sounds like this same problem. I do OK in self-diagnosing engine problems. It is a regular miss, not a random miss, and doesn't occur while it is warming up. It only happens with very light throttle. Sounds like a single coil problem. I'm going to order a set of four coils on Ebay.

 

If they are iridium plugs and the mechanic gapped them they could have been damaged. Most iridium plugs are not supposed to be regapped due to the fine tipped electrode. The other thing that could be is if one of the plugs is gapped differently. Due to the plugs being a fixed gap it is important to measure the gap to make sure one of the plugs hasn't had the gap changed (ive seen this happen when the plugs have been dropped in the auto parts store).