Q. I have a 2001 Toyota Sienna. Lately when starting the engine, there is a fair amount of white smoke. For the last month I was thinking it was nothing more than condensation, but now I’m worried about a possible engine problem. What do you think the problem could be?

A. White smoke is typically a sign of an internal coolant leak. The most common leak is a cylinder head-gasket. A cylinder head gasket leak can be verified with and infra-red gas analyzer or a simple chemical test. If it is determined that the head gaskets are leaking, be aware this is a complicated and expensive job. The “flat rate” time, that is the time it will take most good technicians to complete the job, is about 12 hours.

Q. My 2002 Ford Explorer with the eight-cylinder engine has been stalling lately. The stalling happens while I’m waiting at a stop light. It doesn’t do it all the time, but it is getting worse. The engine light has never come on, and we have kept up on regular maintenance. I’m hoping for something simple like a clogged fuel filter. What do you think?

A. The problem could be as simple as a vacuum leak. A good technician will start with the basics and then scan the vehicle’s computer system for problems. The most common cause of an intermittent stall, without a check engine light, is a faulty idle air control (IAC) valve. This part controls the idle speed and also provides a “soft” return to idle after acceleration. The part, depending on the manufacturer, is about $150 and requires less than an hour to replace.

Q. I own a 2001 BMW 325i with 85,000 miles on it. I just saw a 2005 Acura TSX with 28,000. It just came off of a lease and looks great. Should I switch?

A. In the next 15,000 miles, you will be facing some maintenance expenses in addition to normal wear and tear of a nearly nine-year-old car. The Acura is a great car but, in my opinion, lacks “soul” that is in the DNA of every 3 series BMW. Comparing the two cars, the BMW has about 15 less horsepower than the Acura, but feels more powerful and better connected to the road. If you are looking for maintenance-free sporty performance, buy the Acura. If you don’t mind the repair bills and truly enjoy driving, keep the BMW.

Q. Do you have any helpful suggestions on how to remove the gasoline smell and stain on leather car seats?

A. Gasoline is a solvent and will permanently stain leather. Allowing plenty of ventilation will allow the gas smell to dissipate. Before you try anything yourself to remove or cover up the stain, I would contact an automotive detailing shop or a specialist in leather restoration.

Q. I own a 2005 Jeep Wrangler X with a 4.0L six-cylinder engine with an automatic transmission. I would like to find an aftermarket supplier that has a product that will improve the gas mileage of the vehicle. I would appreciate any information you could make available.

A. I have seen hundreds of additives and devices that are supposed to improve fuel economy and, in my opinion, none of them work. In fact some of these devices actually reduce the vehicle’s fuel economy. I have found that regular maintenance and the driver’s attitude has the most dramatic effect on fuel economy. Keeping your vehicle’s engine well tuned, the tires properly inflated and driving in a reasonable manner will improve your vehicle’s overall miles per gallon.