back fire

My Daughter has 90 Probe LX, she tells me that it started back firing, not all the time, and it seems to happen when she accelerates. Does anyone have any help or ideas to look?
Thank you.

You either have an ignition problem or sticking valves. Most of the time it is an ignition problem. Check the inside of the distributor cap for carbon tracks. Check the rotor for wear or pitting. Replace the spark plugs and wires. Wires that are next to one another can cross fire into another cylinder. If none of that solves the problem I would have the ICM (ignition control module) tested at one of the major parts houses.

If none of the above solves the problem it is probably sticking valves. Automatic transmission fluid is really good to untstick valves. Put a quart of it into the engine oil. Let the engine run at idle for a few minutes to let it circulate good. If you have to drive it do it gently, then change the oil and filter. Tranny fluid is good for freeing up sticking valves, but it isn't a great engine lube so you shouldn't drive on it very much.

I had the same problem with mine. Oil had gotten into the Spark Plug wire throuhg the valve cover. All i had to do was change the Spark Plug wires and everything was good! Haven't had a problem since!