Q. My 1999 Ford Crown Victoria sometimes stalls when I start it in the morning. Starting the engine again with my foot on the gas pedal keeps it from stalling until it warms up. This does not happen all the time and sometimes seems better if I change gasoline brands. But even then it will still stall occasionally. The mechanic wants me to leave the car overnight so he can see the problem firsthand. What do you think?

A. Certainly, leaving the car overnight makes sense. This way the technician can hook up test equipment and measure various sensors when the engine is cold. Possible problems include a faulty idle air control motor, dirty throttle valve or poor connection at the temperature sensor. You didn’t mention how often the car is serviced, and it is possible the car just needs some regular maintenance. A misfiring spark plug or vacuum leak could also be a problem.

Pathfinder’s ‘new’ motor

Q. About two months after I bought a 2003 Nissan Pathfinder, I was on my way to work and the car was having trouble accelerating to highway speed. I managed to get up to 45 to 50 mph, and immediately headed to the dealership where I bought the vehicle. After a couple of days, the dealership said I needed a new engine. Fortunately this was covered by an extended warranty. The dealer put in a used engine; why didn’t they put in a new engine? Is this a problem with Pathfinders or did I get a lemon?

A. The used engine was put in because your truck had a used engine in it. Putting a new engine in your vehicle would be betterment, and insurance companies generally put the vehicle in the condition it was before the claim. They will fix it but not improve it. Your Pathfinder may have suffered from the previous owner’s lack of maintenance. Some older Nissan products with this engine had some oil consumption problems, but I’m not aware of any with the later models.

Impreza has no heat

Q. I have a 1993 Impreza all-wheel drive that is not giving cabin heat. The air is blowing a steady cold, but the temps read normal. Is it the heater control valve, and if so, where is it? It seems that the thermostat is okay.

A. Your car does have a heater control valve; it is located on one of the hoses that connects from the engine to the heater core. A simple way to check this problem is both the heater hoses should be hot. If one hose is hot and the other cold, the heater valve is not operating. The other possible problem is the heater blend door is faulty and not opening and not allowing hot air flow into the cabin.

Is extra warranty worth it?

Q. I just bought a 2008 Nissan Altima 2.5 S. I plan to keep the car for several years, perhaps up to seven if I don’t get bored with it. Is it advisable to buy an extended warranty?

A. I wouldn’t rush into the purchase of an extended service contract. Your Nissan is a covered by a three-year, 36,000-mile warranty and a five-year, 60,000-mile power train warranty. This is in addition to the federal emissions warranty that covers many of the emissions related components.

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