Question - I was driving home from a friend's house and was on my way up a hill when I stopped at a stop sign. After restarting and letting the clutch out on my 1986 Ford Escort GT with 120,000 miles on it, the peace was shattered by the sound of my No. 2 spark plug attempting to be the first such automotive part to land on the surface of the moon. It just blew right out of the engine with an incredibly loud noise. I found the plug lodged in the insulation on the underside of my hood. So I removed the fuzz, screwed the plug back into the block and reattached the wire. After that, the car ran fine.

Do I need to do anything else? And is this a sign that the end is near for this engine, or did my mechanic just forget to tighten this plug during my last tune-up? - RandyTOM: Isn't it amazing how much power spark plugs have when they shoot out of a cylinder like that? I've got about six bumps on my head from similar spark-plug "launchings."

RAY: You mean the spark plugs blew out and hit you right in the head?

TOM: No, in each case, I was napping on the creeper underneath some other car, and the noise jolted me awake and caused me to bump my head on the transmission.

RAY: Your mechanic just forgot to tighten the plug, Randy. He screwed it in with his fingers and forgot to tighten it the rest of the way with the ratchet wrench. And as you drove around, the "explosions" in that cylinder slowly unscrewed the plug the rest of the way, until finally it went kablooey. This is just one good reason why cars have a device called "the hood."

TOM: And as long as the plug wasn't damaged, you should be able to just screw it back in and keep driving. But there is one other thing you should do: Check the other plugs to make sure they're tight.

RAY: There are torque (tightness) specifications for the plugs, and to be sure this doesn't happen again, you want to be sure all of your plugs are tightened to those specs. And always remember to drive with the hood closed.

Question - My car is a '93 Volvo 960. When I first turn on the air conditioner, it gives off an odor which makes me think the car is harboring a well-used cat-litter box. This odor ("stink" is more descriptive) goes away after several minutes, only to return each time I turn on the air conditioner. I've tried air-freshener sprays, but they just introduce a new dimension to the problem. I'd love to take care of this problem before next summer. Any ideas? - Edgar

TOM: Well, my guess is you've got yourself a little mold-spore farm there, Edgar. Congratulations.

RAY: There's a part of the air conditioner called the evaporator, which removes the moisture from the air ("conditions") it. That moisture is then supposed to drain out through a hole in the bottom of the evaporator housing. That's why you often see water dripping out from underneath cars in the summertime.

TOM: My guess is that you don't see much water dripping out the bottom of your car, Edgar, because your drain hole is plugged up. That's preventing water from escaping and creating the perfect breeding ground for mold spores; a dark place with standing water.

RAY: You need to have somebody clear out the evaporator drain for you. It's an easy job and is usually done with compressed air. Then you'd be wise to spray something in the vents to kill the remaining mold spores. There are automotive products specifically designed for this purpose, but consumer products like Lysol seem to work just as well.

TOM: And if that doesn't work, Edgar, then I'd start asking around to see if any of your neighbors cats really have misplaced their litter box.

Question - I live in Spring Hill, Fla., where most of us drivers are over 70 (they sometimes call this God's Waiting Room!). I've enjoyed reading your responses to other people's problems for years, and now it's my turn. My 1989 Buick Century (blue, with sun-and-car-wash-damaged paint) has 160,000 miles. This week, after the car has been running for 30 miles or so, it doesn't seem to downshift very well. When I slow down, it shudders and has twice stalled out. I checked the transmission fluid and added some, but it still did it the next day. What's happening here, and what should I expect to pay to fix it? -Bill

TOM: I think your torque converter clutch is on the fritz, Bill.

RAY: Don't confuse the guy by using technical jargon, Tommy.

TOM: What? Torque converter clutch?

RAY: No. "fritz!"

TOM: Oh. Let me explain, Bill. Modern automatic transmissions have a device called a lock-up torque converter, which locks the transmission into high gear whenever you exceed 35 mph or so (which we know is rare for you guys in Spring Hill, Fla.)

RAY: Why does it do this? To improve fuel efficiency. Automatic transmissions use a fluid connection, and are always "slipping." The fact that they can slip makes it possible for you to stop the car without taking the transmission out of gear.

TOM: If you stopped a manual-transmission car without taking it out of gear, it would do what? Stall, right?

RAY: But that slipping, because it's less efficient than a hard, mechanical connection, does cost you some gas mileage. So the lock-up torque converter locks the automatic transmission into high gear at speeds over 35 mph, as if the transmission were manual. That gives you the best of both worlds.

RAY: And it sounds like your torque converter clutch isn't disengaging. It's as if you were driving a manual-transmission car, got off the highway, and tried to come to a stop with the car still in fourth gear. What would happen? The car would buck and eventually stall. And that's exactly what's happening to your car.

TOM: So, normally you would fix this by replacing the torque converter, which requires taking apart the transmission. But since your car has 160,000 miles on it, and its future is even more in doubt than yours, Bill, you might consider just unplugging the torque converter clutch, which does not require opening up the transmission, and takes only a few minutes. Your mileage may get a tiny bit worse, but you won't notice any other difference in performance.

RAY: Some mechanics may try to convince you that damage can eventually be done to the transmission by just unplugging the torque converter rather than fixing it, but we haven't seen any proof that that's true. And besides, after racking up 160,000 miles on this car, you've earned the right to do whatever you want, Bill.

The Magliozzi brothers' radio show "Car Talk" can be heard each Saturday at 10 a.m. on KUER FM 90.1 If you have a question about cars, write to Click and Clack Talk Cars c/o King Features Syndicate, 235 E. 45th St., New York, N.Y. 10017. You can e-mail them at http://cartalk.com