Dear Doctor: I have a 2003 Subaru Forester with the automatic transmission. It has a bad miss during warm weather conditions and it feels like the car is jerking. However, when I get a full tank of gas, the jerking stops, until I've driven 100 miles and then the jerking resumes. A "check engine" light is not set. Can you help?
Dear Virgil: It seems like a fuel issue. A full service inspection is needed, beginning with a road test with a professional scan tool and fuel pressure gauge that monitors the engine computer inputs. A qualified technician will be able to compare the vehicle information and known good values and compare those values with your Forester.
Dear Doctor: I have a 2010 Ford Edge with 49,000 miles. My heater fan stopped working so I took it to the dealership where they told me the fan relay has gone bad. They replaced the relay and then discovered that the fan motor sounded like it had a bad bearing -- and that I needed to replace the fan. Should the fan have worn out this quickly?
Dear Bettye: This is not unusual failure for any vehicle brand. Most blower motors are located low in the heater box and are subject to moisture, as are many blower resistors. Your Ford, even with its low mileage and age, is subject to moisture as well. I see a lot of blower motors and resistors having to be replaced, including the wire harness connector.
Dear Doctor: I have a 1993 Ford Taurus SHO with the 3.2-liter engine and automatic transmission and 144,000 miles. I'm now hearing a popping noise from the engine at 3,500 rpm while sitting idle and revving the engine. I've always used 5W30 Pennzoil or Motorcraft. Any advice?
Dear Harold: Most engine computers do not allow the engine to rev up past 3,000 to 3,500 rpm in park or neutral in order to prevent engine damage. If the engine runs as designed and revs up to the redline in gear while the car is moving, then the computer and engine are working as designed. If there is a popping sound while driving the car, then an engine compression test is required.
Dear Doctor: I have a Cadillac DTS with 31,000 miles. Most of the time I do not start it for weeks. When I do start it I sometimes hear a loud pop from the dashboard area. Could you tell me what this is?
Dear Ben: The loud pop sound is most likely from a sticking heater/air conditioning blend door moving from its position. The dash cluster and all of the gauge components are electronic and have no moving parts, so it would not be coming from the dash area. You may also want to ask the service writer at the dealership if they've had any other inquires on this sound.
Dear Doctor: I own a 2010 Honda CR-V with 41,000 miles. I use synthetic oil and change the oil every 3,000 miles or three months. I drive the car mostly around town. I would like to know what you would recommend the oil change interval be.
Dear Joe: Vehicles that are driven on local and short trips need to have the oil changed more frequently, because of all the acid and moisture that develops in the engine. The vehicles that are driven on the highway are at operating temperature for a longer time and will burn off any moisture that would collect in the engine. For your driving habits, I suggest twice a year -- spring and fall -- with full synthetic oil.