The oil level is not likely the cause of the problem. If it was we would hear about this a lot more often. The clue is the gas smell from the exhaust. If you have access to a scanner that can read live sensor data, the place to start is by looking at the MAP sensor reading. It will be listed as a voltage and as inches of mercury. When you first turn on the ignition switch, it's reading is recorded as the barometric pressure. Once the engine is running, it's reading is the intake manifold vacuum. Those two readings are the biggest determining factor in how much fuel enters the engine. The sensor is supplied with 5.0 volts and ground. The signal voltage must be within 0.5 and 4.5 volts. If the sensor is starting to fail, it could report the wrong value, but as long as it's within the acceptable range, no diagnostic fault code will be set in memory. That's where using the scanner can help. Higher manifold vacuum results in a lower voltage from the sensor. If the voltage is too high, say 2.0 volts or higher, at idle, that is telling the Engine Computer the engine is under load and more fuel is needed. Be sure the small vacuum hose to that sensor is tight and not cracked.
You might also try connecting a timing light to see if the timing is bouncing around. This really shouldn't be an intermittent problem, but if it is bouncing all over, suspect worn bushings in the distributor.
Don't overlook the ignition coil. Mine caused the same problem you're describing for 11 months before it finally failed completely. At first it acted up worse on hot days, and it always ran better at highway speeds, presumably because the air flow cooled it down. It would totally stall after driving around at slow speeds like in a parking lot, then could be restarted in less than a minute. By the time I got under the hood to check for spark, it was already working. That's what made it so hard to find.
Saturday, February 12th, 2011 AT 9:52 PM