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Q: I just purchased a 2014 Chevy Equinox that uses synthetic oil. The owner's manual tells me a light will come on when it is time to change the oil. This makes me nervous. I know someone with this same vehicle who had to replace the engine due to not enough oil changes even though they were done when the light came on. I put on about 2,000 miles a week. How often would you suggest to change it?

A: Your vehicle, like so many modern automobiles, is equipped with an oil service monitor system that calculates when it's time to change oil and filter. By electronically monitoring a number of parameters including number of engine starts, rpm, manifold pressure, oil temperature, coolant temperature, throttle position, etc., the system determines the correct mileage and time when the oil should be changed.

Interestingly, I found no specific mileage recommendations for engine oil changes in either my ALLDATA automotive database or the specific owner's manual for that vehicle. Both sources indicate oil should be changed when the oil monitor system illuminates the "Change engine oil soon" warning light. Since you put 8,000 miles per month on your vehicle, I would suggest resetting the oil monitor system at the next oil change and driving until the warning light illuminates that it's time to change oil. Check how many miles you've driven. I wouldn't be comfortable driving much more than 10,000 miles between oil and filter changes.

Q: I want your opinion on an issue with my 2016 Suburban. I brought it in for a vibration about a week after I bought it and was told that when the engine went into V4 mode from V8 mode, the exhaust system will vibrate the whole time. It's noticeable at 25 to 50 mph. Chevy says this is a normal condition, they all do it, but is looking for a fix for it! What are your thoughts on this?

A: I researched this issue with 2015-16 full-size GM trucks and SUVs. Some of the data indicates the possibility of a low rpm or idle vibration from the exhaust, possibly caused by a loose exhaust heat shield mounting stud. But most of the info points to wind buffeting/pressure pulses originating from the roof area. GM issued preliminary information bulletin PIT5318B outlining the procedure for checking the bond between the roof reinforcing bows and the roof sheet metal. The concern is that if the bond has separated, the roof will vibrate, causing pressure pulses similar to what's felt when the rear window on a sedan is opened partially while traveling at speed.

Because of the relatively low speed at which you experience the vibration you might want to ask the dealer if he has seen GM service bulletin PIP5211 suggesting checking and realigning engine mounts to correct this issue.

Q: I am the original owner of a 2006 Acura TSX. For the past year the car has not idled well and a message on the dash tells me to check the emission system. I brought the car to a mechanic and had two O2 sensors and all four spark plugs changed, along with a valve adjustment. This did not remedy the problem and it still idles poorly and the light continues to stay on. What are your thoughts?

A: My "old school" diagnosis would be to check for some type of induction air or vacuum leak. And I'd still begin with a careful visual/physical inspection of all the air intake plumbing and vacuum hoses and fittings. Also, check the fuel cap very carefully. If the cap fails to seal properly, an emissions warning light will illuminate.

Have you or a technician cleaned or replaced the throttle body? If DTC fault codes P2279 or P0510 are stored in memory, the throttle plate closed position may need to be relearned by the powertrain control module (PCM).

Paul Brand is the author of "How to Repair Your Car" and "How to Repair Your Truck and SUV," published by Motorbooks.