Q&A

First and foremost, inspect your spark plugs and ignition wires. If they are more than 60k old, they may need replacement. This is the first issue I check when a car misfires under load. As the engine heats up, the mixture gets leaner and it takes more voltage to ignite it.

Back firing is usually a sign of the air/fuel ratio going lean. To find an intermittent problem like this I "tee into" the fuel line and tape a fuel pressure gauge to the windscreen so I can monitor fuel pressure when the problem occurs. I also drive around with a timing light attached to one of the spark plug wires, when the vehicle falters I pull the trigger on the timing light and see if I have spark if not I check the ignition system and wiring and sensors associated with the ignition system. If uncertain about the spark plugs replace them, inspect the color and condition of the plugs you take out. Intermittent problems are hard to find and your vehicle has limited diagnostic capabilities. Understanding how each system works, having a good wiring diagram and volt/ohm meter and patience are required to trouble shoot this kind of problem.

My car had similar symptoms. There is a electronic air-flow valve that sits on top of the air intake that regulates the air flow when the vehicle is idling. I was able to remove the valve and clean it with carburetor cleaner. The car now idles nicely and only stalls when my daughter dumps the clutch at a red light.