Q I have a '94 Lincoln Town Car with 111,000 miles on it. It runs real well, except I get a skidding sound from the front if I put my foot on the gas pedal too fast or climb a steep hill. Also, there's a small vibration in the front when going up a hill. The skid sound reminds me of those strips on the highway as you approach a stop sign. Could it be the transmission?

A You're close. You're describing a shudder from the torque converter clutch slipping as you apply a load to the transmission when accelerating. The converter clutch is designed to lock the torque converter by applying a hydraulic pressure differential to the clutch, forcing it against the case of the converter and eliminating any slippage. After many years and miles, the seals on the hub of the converter are likely worn to the point of not being able to generate and hold that pressure differential, allowing the clutch to slip. Try adding a can of SeaFoam Trans-Tune to the transmission fluid; this might help the seals function better and hold the clutch engaged.

A complete drain/flush/refill/new filter for the transmission may help the problem, but if not, the long-term fix is to replace the torque converter, which is probably not cost-effective for your vehicle.

On another note, an engine misfire from a bad spark plug or ignition coil can generate a very similar shudder.

Q I have a 2003 Chevrolet TrailBlazer that has an engine vibration when the engine is cold and the car is in gear but not moving. After I drive it about 20 minutes, the vibration disappears. It does not vibrate when the car is moving. Can you shed any light on this problem?

A Does the "check engine" light illuminate? This vibration could be a misfire when cold. A diagnostic test with an electronic engine analyzer during a cold start-up might pinpoint an issue like this. Another possible cause could be a failed engine or transmission mount.

Q I own a 2010 Chrysler Town & Country. When driven over driveways or the body is torqued, the two rear sliding doors creak. It has gotten worse as the weather gets colder. The dealer says there is no fix because there's no way to adjust the doors.

A My Alldata automotive database pulled up the "sliding door adjustment" page in Chrysler's service literature that outlines a detailed series of adjustments for the sliding doors, including adjustments for flushness, door gap (up/down and fore/aft), door seal compression, stabilizer and front striker adjustments.

But why not start with the simple stuff? Directly spray the sliding door gasket/seal with an aerosol silicone lubricant and clean the gasket mating surface on the inside edges of the doors. This may eliminate much of the squeaking.

Q For a couple of years now, the left front headlight on my '05 Prius will suddenly switch off but eventually come back on. The Toyota dealer said that because it was working at the time, they couldn't diagnose the problem. Now the right front headlight is doing the same thing, and I'm afraid they both will go off at the same time. Any suggestions?

A A Toyota technical service bulletin, TSB-0030-08 dated April 2008, outlines the testing procedure for intermittent operation of the HID (high-intensity discharge) headlights that includes voltage-drop tests and a check of the 12-volt connector to the HID control unit. If all this checks out OK, the problem may be in the HID control unit.