Visiting Pops now. HE does not drive since late July, and did not drive much for long stretches this year. He still has his car, which I use when I visit. An old Altima (mid to late aughts). At any rate, the last time I gassed it was in early August. I drove it for a week or so, short distances, in early September. Now I'm visiting, and the thing runs OK the first drive in the AM (about a mile), but then is pretty rough when idling on the return trip. Idiot check engine light flashes. Is this likely crud settling out of the gas? Could it be vapors in the tank? Water? Ideas?
Bad gas would be a prime suspect. Ethanol blends are notorious for breaking down and creating water vapor, which sinks to the bottom where it's readily accessed by the engine. Further, the process of creating water reduces octane. So if 87 octane was used in a car that's supposed to use 87 octane, by now the gas is well below the minimum recommended. Run the car real low, siphon out the rest to recycle (Fairfax County dump accepts petrol products, maybe yours does too) and when you refill, go easy - don't put a 5 year supply in the tank. Put a small amount and add fuel stabilize, and use a higher octane gas.
