Q. I have a 1999 Mercury Mystique with 80,000 miles. It runs well and has no problems—until I have the oil changed. Soon afterwards, the engine stalls while I’m driving. It happens sporadically and lasts one to two days; after that, everything is fine. Since I am due for another oil change, do you have any suggestions?

A. The oil seems to be the only common denominator. Some Ford engines are very fussy about oil type and filters. This engine uses a variable camshaft that requires a specific oil filter and oil. The Ford filter has an internal check valve that keeps the exhaust valve closed in order to prevent stalling. At the next oil change, ask the garage to use 5W-20 weight oil with a factory style filter.

Q. The gas gauge on my Chevy Tahoe always displays “empty” regardless of how much fuel is in the tank. I was told that the problem stems from a chemical build up on the sensor. I’m trying to avoid the expense of removing the gas tank. Is there a gasoline additive that can clean the fuel gauge sensor?

A. If the gauge always shows empty, I would check the gauge circuit first, and then move to the sensor. You are correct; in many cases, the fuel level sensor fails as a result of the deposits in some gasoline formulas today. The sensor is not serviceable and will need replacing. I have some good news, however. Unlike many vehicles, this sensor can be purchased separately from the fuel pump.

Q. We have a 1998 Toyota Camry with 165,000 miles on it. We love the car and haven’t had trouble with it until this past winter when it began to stall. Usually this would occur in traffic. Other times, I would have difficulty starting the engine. I have had the oxygen sensor and the fuel filter replaced. These repairs worked for a while but it began stalling again. The mechanic suggested that the idle air control motor be replaced. They weren’t sure if that was the problem, however, and we didn’t want to spend $800 and fail to solve the problem. The Camry has not stalled since the weather has warmed up. Do you have any suggestions on what it could be?

A. There are three areas to investigate. The first is the ignition coil. Many of these coils fail with age and cause a similar symptom. The second is the coolant temperature sensor, and then the idle air control valve. The estimate on the idle air control valve seems a little high.