Hi Everyone:

I have a 2018 Grand Caravan GT with 8,000 miles. Runs great at all times and the idle is as smooth as glass to the point where you can't tell it's running at the lights. With the exception of when you are sitting at a light on occasion (not all the time) and it feels like it has a slight stumble. If you ease up on the brake to where you just start rolling forward it feels like an ever so slight miss similar to the reverse shudder that it common with the 62TE but just less pronounced.

There is no Check Engine light and no codes stores (OEM or OBD-II) so I'm not sure what's causing it. It didn't do it when it was first new and developed in the last few thousand miles. Hasn't gotten any worse or any better. I'm using Top-Tier fuel and have tried different brands and stations and with ethanol and 0 ethanol.

Fuel economy on it is similar to our 2012 Caravan that has 300K on it now and idles smooth and our 2017 in the family with less miles, so I'm not sure why mine doesn't.

The only thing I can see that doesn't make sense to me is the L/T fuel trim at idle for bank 2 is approximately -7 and bank 1 is -4 Other than that the readings from all inputs (sensors) match my father in-laws 2017 Caravan which also is smooth at idle with no occasional slight stumble at idle.

Thoughts?

 

If you can duplicate it, take it in and use your warranty.

 

I have had it in already and because it's not storing codes they won't do anything about it, I took it to two dealers. I even video taped a cup of water on the dashboard when it's normal and when it's doing it and you can see the difference. The tachometer also moves up and down every so slightly as well. Showed this to them and get the standard line meanwhile the 2017 and 2012 we have in the family do not.

 

Some further information... One bank of cylinders post catalytic O2 sensor goes lean after idling for a minute while the other doesn't. Both upstream are cycling and match each other more or less and LT trims are below 10% and ST trims are below 4% both banks match each other. Both catalytic converters will show 0 when coasting as it goes open loop so the sensors are responding. I'm thinking maybe a bad O2 sensor up-stream on the one bank driving the mixture too lean on that bank of cylinders as indicated by the catalytic O2 sensor going lean?