A random what?

So, you entrusted your car to a professional to tell you what was wrong, and...you never asked him what was wrong.

Instead, you came HERE to ask what was wrong.

One or more cylinders misfiring. "Random" means that the PCM could not yet identify exactly which cylinders were involved or, the system itself isn't capable of making the distinction.

Entirely possible but a little moisture shouldn't have an effect on how the engine runs i.e., misfires.

The guy sounds trustworthy in that he didn't go directly for the jugular...

If you get a check engine light again, ask him what error code(s) he found and post that info here.

One of the things that the Check light tells you is that the battery went dead.

Nevermind, I didn't read long enough to get to the Random Misfire code.

Having said that, the random misfire could have been stored much earlier, AND the mechanic didn't bother to tell you that there was a report that the battery had been disconnected, so if this is the car we have been discussing the battery issues on, then the Check light could be from that problem not the stored misfire report. I'm not sure that a random misfire will illuminate the Check light. Hmmm...

Actually the Check Engine Light tells you way more than that. One of the things it tells you is that the battery has been disconnected. There is a code for disconnected battery.

Some of the things are transient, and ignoring them is a reasonable thing to do until you get a repeat. Some things are important to have repaired immediately, that is certainly true.

He told me there could have been a misfire. ( wow ) But why? He didn't know. So if it can happen once in awhile by accident(?) how come the computer keeps codes for it and lights up the dash?

The question remains, as to why something which sounds trivial, would have the computer lighting up potentially costly warning lights.

The other car.

The only real thing I;ve noticed since the weather got colder, is that until the engine warms up, I'm hearing clickety sounds when I step on the gas, from the firing or something inside, but it's not coding because of it. May be something, may be nothing - just a quirk of this model?

If it's the former, why leave the light on?

Your mechanic may have lead you to believe that what happened is trivial, I wouldn't relate it in such terms to one of my customers.

Something failed to cause the random misfire(s), the only way to determine why is to perform some testing to come up with a diagnosis and a plan for repair.

Moisture related misfires are often related to the secondary (high voltage) side of ignition system. Plugs, wires, cap and rotor if so equipped, ignition coil.

Because it detected a failure.

If a predetermined number of no failure run cycles occur, the light should go off.

Most of this should be covered in your owners manual. Have you read it?

Those are interesting things to have go bad. It snows where she lives. She might want to pay closer attention to the warnings being sent by her car, lest she end up freezing to death on the side of the road.

The transient stuff will generally turn the light off if the condition corrects itself. For example, there is notghing wrong with driving around (from the perspective of the health and well being of the car) with the Check light on because the gas cap is laying in a gutter someplace, or installed but not tight, or operating with leaking parts inside. A gas cap can be corrected by simply putting it back on, but the code will be stored and the light will remain on for a few drive cycles so the car can be sure the system is working right.

You might pull the codes before the light goes out, but you could just as easily fix the problem and the light will go out by itself. Or, you could pull codes and do nothing other than screw the cap on tighter on the next fill up, and reset the code and wait for a repeat.

A random misfire could be caused by any of a dozen different things, and could happen once then not happen again for a long time. Or it could happen again tomorrow. Some codes are transient, some are aged (they happened at some unknown point in the past).

Sometimes it is a reasonable troubleshooting strategy to log the codes, reset the computer, drive for a while to see if the prior codes are an actual problem, or were transient. If an actual problem, the Check light will come on again. You pull the codes and see if what is reported is the same as what is on the log you made previously. You focus on the new codes that are also on the log.

Random Misfire means that any of the cylinders misfired. You don't know which one, so it would not be prudent to buy a set of plug wires and box of plugs because the Mass Air Flow (or whatever sensor they use to do the equivelent job) tells the computer what the air density is, and the computer sets the injector timing by some algorithm to try to create the perfect air/fuel mixture for the air density.

If the air density reports are not accurate, then the fuel mixture can become lean enough that the work expected by the firing of a spark plug is not performed, so the speed of the crank is not what the computer expects, and the computer says, "there must have been a misfire," so the light comes on. If the misfire is always on Cyl. 1, then the report is P0301 MISFIRE CYLINDER 1. But if the misfire is random, then the report is P0300 RANDOM MISFIRE. A misfire on a particular cylinder is a sign of a wire, coil, plug, some particular part. A misfire that's random is usually not a plug or a wire or a particular part of the Ignition System.

A reasonable troubleshooting techinque is to reset the code(s) and wait to see if it returns. Another strategy is to start buying shopping carts full of parts and loading your shotgun to see if you can get the light to go out.

That's a bad idea. The computer can be damaged, and then you have a whole new set of problems to solve.

Which car is this, your '93 or the '02?

You are hyper-sensitve to normal automotive sounds. I liken you to the mother that stresses out at the first random cough of her child, and rushes to the doctor for a check up because the kid sucked down some floating lint that tickled his throat and caused him to toss out a cough or two.

Since it is getting colder, the oil thickens. Since the oil thickens with cold, it doesn't pump very well, and the _tiny_ orifices that the oil has to flow through to get into and out of the hydraulic lifters (parts that open the valves) can become clogged with residue of aged oil. Basically, you can hear valve noise until the engine warms. You could hear lots of noise until the engine warms, but there's no need to go to the doctor (mechanic) because of them.

What you really need is a car with greater sound deadening qualities built into it.

Yes, the question is, whether what I'm hearing is harming the engine.