Maybe water in the gas

[Dom]

I ran my 91 525i about a month with the tank less then full, hoping that prices would go down.
I then filled up and the next morning experienced a miss in the ignition. When I run it up to operating temp. everything is fine but when cold it misses and seems to run and 5 cylinders.
I'm ready for a fuel filter change, spark and tune up does anyone think this will help or an idle control sensor whatever has to be changed. Or gas drained. plug.
It was running great. I'd appreciate any help. --- Dom

[shogun]

to get water out of the tank there are additives, these bind with the fuel and then they leave your car at the exhaust.

Gas treatments contain solvents and alcohol that remove water from the gas via chemical reactions.

Read more: How to Remove Water From Fuel | eHow.com How to Remove Water From Fuel | eHow.com (http://www.ehow.com/how_5252268_remove-water-fuel.html#ixzz1KzphpoJ6)

or the DIY way:

If you only have a small quantity of water, then the addition of 500mls of dry isopropanol (IPA) to a near-full 30-40 litre tank will absorb the water, and will not significantly affect combustion. Once you have mopped up the water with IPA, small, regular doses of any anhydrous alcohol will help keep the tank dry. This technique will not work if you have very large
amounts of water, and the addition of greater amounts of IPA may result in poor driveability.

Water in fuel tanks can be minimised by keeping the fuel tank near full, and filling in the morning from a service station that allows storage tanks to stand for several hours after refilling before using the fuel. Note that oxygenated gasolines have greater water solubility, and should cope with small quantities of water.

[Tiger]

Today's gas in USA has ethanol in it... over time... it will separates into alcohol and water. Usually they say no more than 2 months... so I don't know... Star tron makes fuel additive that prolongs the fuel. Stabil also makes similar thing. I think it is pretty necessary these days especially for small engines... where we don't use it that often.

They say to drain small engine fuel tank but I am not a favor of that... things will dry rot if not rust because of little water we can't get out... so I highly recommends using fuel stabilizer and keep full tank in small enignes... make sure you run it with treated fuel to make sure it goes through the entire fuel line system.

[ScottyWM]

If you're ready for spark plugs - you're probably past ready. How long since they've been changed? I'd start by looking at them. Years ago I had a slight miss like you describe, changed plugs and all was fine. I've gone almost empty on fuel too many times but never had a misfire upon fill-up. Are you sure you put the gas cap back on?

You don't have the valve cover gasket leaking onto a coil/plug do you?

[Ross]

Today's gas in USA has ethanol in it... over time... it will separates into alcohol and water.

I've never heard of this. To the contrary, fuel "driers" are predominantly methanol, which is very similar.
E34s have a drain in the tank and water is heavier so there's an easy solution if there is water in the fuel.