03 malibu miss at idle

My malibu 3.1 V6 has a shudder or miss when idling. It only does it sometimes usually when less than 1/2 tank of gas. Does not set a check engine light. When it starts this and you are pulling away from a stop sign or a parking place it causes a hesitation when accelerating away fro a stop. So far no one seems to have a clue what it could be.

If it actually is dependent on the quantity of fuel in the tank then it could be fuel delivery related. But it could also be a simple as adding some alcohol to the fuel to absorb a large amount of water in your tank which gets sucked up when the fuel level gets lower.

A miss at idle can be caused by one of the coil packs going bad and the half tank thing may be a coincidence. I had to have one replaced at 45,000 km because it caused an miss at idle.

I have also had to put alcohol in all our vehicles from time to time to get the water out that condenses in the tank from driving in and out of heated garages into freezing temperatures.