About a year and a half ago, my car suddenly cut out when stopped at a light.
The exact problem is, I'll be sitting idling, and if I sit there idling too long, sometimes (not always), the idle will start fluctuating, racing too fast, then dropping to too low, then bouncing back to high, and after a couple of iterations the "too low" bounce will make the engine stall. I have gotten decent at hearing the sound and throwing the automatic into park, putting foot on gas, and essentially manually keeping the car from conking out by keeping the engine racing faster. When the stop light changes, I have to throw the car into drive and hit the gas quickly to keep the car from stalling.
Once this problem has started, it doesn't usually stop. Sometimes I'll sit in a parking lot and just keep the gas peddle pressed down for several minutes, and there'll be a pop(it's not realy a sound, but I can feel the gas pedal versus revs dynamic changes) and if I release the gas pedal the car will go to an idle that doesn't require me to manually keep it going.
Since that time, this is an intermittant problem that has been plagueing me. I took it into the dealer within a couple weeks of the problem starting, and they gave me the "it's an old car, it could be anything". Gave it a tune up, replaced the battery, and replaced an engine gasket (sorry, forget exact name). It didn't fix the problem. Last December (before driving it 350 miles for holidays) I took it into a mechanic shop that a coworker had suggested. The car, of course, didn't do it's thing while they had it, so they couldn't diagnose the problem.
Luckily I live within walking distance of work, so the only times I drive the car is about once a week for groceries and once a month downtown to pay my rent.
I cannot seem to find a consistant, predictable list of conditions as to when this happens. It *seems* to happen more frequently when it's raining/high humidity, or if I haven't let it warm up all the way before taking off. Letting the engine fully warm up (as in, temp gage in the middle) is not a cure. It will still do it even if the car is warmed up all the way. In fact it's often times a worse problem if I've been driving it around off and on for over half an hour, as the conking out of the engine is NOT proceded by the revs fluctuations. I'll just be sitting at a long light, and it'll go from ~900revs down to less than 500 and boom! hello restarting the car).
When the car dies, it generally starts back up. If the stall happens right when the light turns green, it will sometimes act flooded, but I've gotten into the habit of if the car dies to just count to 5 or so before trying, and that usually does the trick...however, the start is usually very rough, as in, there is no idle, it requires me to press the gas pedal down to keep the car from dieing again.
I'm very poor, so I can't afford to just let mechanics "guess" for $500+ a pop without it fixing the problem. The car has 110K miles on it, I am the only owner, and while not a perfect good keeper, I have always gotten the oil changed and taken it in every 30k miles or so for tuneups. I definitely can't afford a new car, and picking up someone else's bad apple doesn't seem like a solution. I'd rather just fix the one I have =/