See more of the story

Q We have a '97 Buick LeSabre that stumbles on acceleration and seems to be getting worse with time. We bought it in April, and it barely did it then. The car has 153,000 miles on it.

The stumbling shakes the whole car, and it's the worst at 1,500 to 1,700 rpm and about 40 miles per hour. Lately it does it even at 60 to 70 mph quite often, whether it's in overdrive or in third gear. If you put it in third, then it's more like 2,000 to 2,500 rpm when it vibrates.

We have had a super mechanic check it out, but he floored it, and it wouldn't do it then. The "check engine" light has come on once or twice, but gone off again, so we don't know if any fault codes would show up if we scanned it.

My husband is wondering if it could be the torque converter, but he's wondered about injectors, the coil pack, or other scenarios as well.

A Hats off to your hubby -- he's the "super mechanic." His concerns over the torque converter are right on the money. Most likely, the torque converter clutch is slipping as it engages, generating the shudder you're experiencing. The quick test is to create the shudder by gently accelerating up to and holding about 40 mph, and when the shudder starts, lightly depress the brake pedal about half an inch with your left foot while holding the speed steady with your right foot. This will disengage the converter clutch, so if the shudder stops then starts again after releasing the brake pedal, you've pinpointed the problem.

You can try adding "Lube-Gard" to the transmission fluid to improve the fluid's lubricity and performance, but if this doesn't help, the torque converter needs to be replaced.

Q I've got an '88 Cutlass I bought new. It now has about 400,000 miles on it. The problem: You start it and it runs fine, but the minute you step on the gas, it kills.

The garage is having a tough time finding the problem, and we've replaced a number of parts to no avail. The mechanic said it's not the gas supply because it's got gas up there. My grandson needs this car to go to school, unless you think it's not fixable.

A Having fuel available and having enough fuel pressure are two different things. Have the mechanic check the available fuel pressure, because it sure sounds like the engine is running extremely lean. Fuel pressure should be in the 35 to 50 psi range, depending on which V6 engine it has. If it's the four-cylinder, look for about 10 psi.

The other possibilities include a weak coil, ignition module or crank sensor. Connect a timing light to one spark plug wire while the engine's idling, then step on the gas while watching the flashing light. If it stops, the ignition is dropping out. If it continues to flash, it's a fuel delivery issue.

Q I've had a repeated problem with the right- and left-side brake light bulbs on my 2003 Pontiac Montana. On two occasions the bases of both bulbs have melted at the point of connection to the 12-volt wire. Could the problem be a short circuit? A poor connection to the bulb?

A Service bulletin 08-03-42-007A in my Alldata automotive database identifies the problem as moisture migrating into the lamp housing, changing the resistance of the bulb and causing the bulb to burn out -- and potentially damaging the circuit board. Replace the bulb, and circuit board if necessary, and apply dielectric grease to the bulb terminals.