Dear Jim,

I have a 1999 Toyota Corolla (dual overhead cam, 1.8 L, 16 valve, 4 cyl.) and the transmission is starting to jerk. It's not a very strong jerk yet, but I'm worried because it seems like it's getting worse. Someone told me the problem could be in the engine, but the transmission is totally separate, right? Am I going to need a new transmission? This one doesn't even have that many miles on it yet.

--Drew Morford

The engine and transmission are two separate systems, bro, but they're connected like the foot bone's connected to the ankle bone. The transmission gets its shifting cues from the engine speed. If there's a misfire in the engine -- and you probably have one here -- that's going to affect the engine RPMs, which is going to give the transmission some weird information about when it should shift gears. As a result, a hard jolt gets applied to the transmission's input shaft and splines, especially when the torque converter kicks in with third gear.

Take your Corolla to a reputable shop and have them put it on a scanner that checks for engine misfires. Chances are, this can be traced to a bad spark plug. If this is the case, the iridium plugs your car uses run about $20 each and you should replace all four.

It's possible, though, that the spark plugs are fine, and that the problem is with a bad engine coil ($150) or a bad fuel injector ($20).

So your transmission might be OK right now, bro, but it most definitely won't be for long unless you get this engine misfire fixed. That constant jolt to the system can do a lot of damage in not much time.

Tip of the Week:

Drivers, check that radiator cap under your hood, especially this time of year. Here's why: The higher the pressure in your radiator, the higher the temperature it's going to take for water to boil. In fact, for every pound of added pressure, the boiling point goes up three degrees. The average cap adds 15 pounds of pressure to your coolant system, which means the boiling point of your radiator water goes from 212 degrees to 257 degrees. Radiator caps cost only about $5 to replace, and those extra 45 degrees can make a big difference when it comes to engine overheating.

Buffalo Jim, owner of Allstate Auto & Marine Repair in Las Vegas, writes a weekly column. Send your automotive questions to him at buffalojim@lasvegasniftynickel.com. If Jim picks your question to answer in Nuts & Bolts, you'll also be the proud recipient of a deck of official Buffalo Jim playing cards, presented in a classy, tin box bearing his hairy image.