Dear Doctor: I have a 2007 Buick LaCrosse with the 3.8-liter engine. Upon starting when the engine is cold it turns over with no problems. However, when the engine is warmed up and has not reached full operating temperature, if I stop and restart, then the engine stumbles before evening out --  or it just stumbles and stalls. I get a strong smell of gasoline when this happens. What is causing this?

Dear Pete: A problem like this requires a professional scan tool. A check of all sensor values is needed to see where the fault lies. A sensor could be out-of-range and not set a fault code, which is why the technician will look at all the input sensor information and check whether the EVAP system valves are working as designed.

Dear Doctor: I have a 2008 Pontiac Grand Prix with an intermittent loss of power steering. The fluid has been checked and changed, and the speed sensor replaced -- all to no avail. Any ideas?

Dear Bill: The most common problem is a sticking pressure valve in the high pressure side -- a return line seal that does not leak fluid, but actually allows air to be sucked into the pump, causing a loss of the power assist. Make sure you use the correct power steering fluid.

Dear Doctor: I have an air conditioning problem with my 1992   Corvette. The a/c works for one day before a light flashes on the temperature control panel and then the a/c fails. It has a read-out as "no Freon", but when I disconnect the battery and hook up the read out unit to the car the reading comes back as "Freon is full."

Dear Guy: Your Corvette's air conditioning system has electronic sensors. If one sensor is out-of-value, then it shuts the system down. My first step would be to connect the pressure gauges to monitor the high and low pressures. I would also make sure the electric fan comes on when the a/c compressor comes on. Find a repair shop that uses both Identifix and Alldata for technical information.

Dear Doctor: I had my 2002 Honda Accord transmission replaced with a remanufactured unit at a local transmission shop at a cost of $2,700. The shop manager told me that five-speed and six-speed automatic transmissions are more expensive due to the increase in number of parts in those transmissions. He did not mention Continuously Variable Transmission models. Do CVTs need to be replaced more or less often than "traditional" automatic transmissions? Are CVTs more expensive than four-speed transmissions to replace? Do shops rebuild CVT models, or can you only get professionally remanufactured ones?

Dear Chris: Transmissions are expensive to rebuild and replace. The later the model year and the more gear speeds, the more expensive they are to repair. Honda has had automatic transmission problems for many years. The CVT is no exception to failure and is also expensive. When a my customers have failed transmissions I give them three options: 1) a factory rebuilt unit with a warranty that is usually 3 years/50,000 plus miles; 2) go to a local transmission shop for an overhaul and a 1-year/12,000-mile warranty; 3) find a used transmission from a salvage yard.

Dear Doctor: I have a 1996 Chevy Tahoe 4WD with the 5.7-litre engine and 128,745 miles. Sometimes when I step on the brake the pedal goes to the floor. If I pump the pedal then the brakes come back. I have replaced the master cylinder four times and replaced the steel brake line wheel cylinders, brake pads and linings, calipers and rotors. I still have this recurring problem. Please help.

Dear Joe: I have owned many General Motors' trucks over the years and have seen all kinds of problems. When a brake pedal drops to the floor many different issues could be indicated, including air trapped in the system, an internal leak inside the master cylinder, anti-lock brake system leaking internally, a frozen caliper slide or caliper piston, or a problem with the rubber brake flex hose.

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