Idle acting crazy

I have insulated my fuel lines by splitting another fuel line & zip tying it around the ones on the car with the split facing up to allow heat to dissipate. I really do not understand why it clears up in idle, it is weird. It is not like the idle is too low & I have to put it in neutral every time I stop just when I get stuck at a long light. I do not touch the gas pedal at all, just slip it into neutral & the idle slowly starts to recover.