Doug McAllister/Under the Hood: Most vehicles have two air filters
Q. The dealer I always take my car to sent me an email saying On Star had emailed them about a problem I’m having with my car. The problem is with the engine air filter. The check engine light never came on. What is the engine air filter? Is that the regular air filter that you change every six months?
A. On Star monitors will vary a little from vehicle to vehicle. It can alert you to what system failed when a SES (service engine soon) light goes on. However, since your light did not go on, I am not sure what the onboard computer is seeing. If an air filter is bad enough to impeded the air flow, you might have some drivability issues and perhaps a SES light on.
The engine air filter keeps dust and debris from being ingested into the engine, keeping wear to a minimum. There is also a very sensitive sensor known as the Mass Air Flow Sensor that is protected by the air filter. Regardless, it would be a great idea to have the air filter physically inspected. A dirty air filter could affect your fuel economy and with these high gas prices, it’s good to squeeze every drop of gas we can out of a tank.
If you are changing your engine air filter regularly and On Star is alerting you based on a time and mileage interval, you may be out of sync with them.
The other air filter present in most cars today is the cabin air filter. This is sometimes referred to as a pollen filter or an HVAC filter. This filters the air coming into the vehicle’s cabin and is commonly forgotten about. This filter can become quite plugged and can really affect the efficiency of the heater and air conditioner.
The best test for both of these filters is a visual inspection. If either of them has excessive debris in the filter material, a replacement is recommended.
Q. I have a 2000 Honda Accord and I’m having issues with the idle. I have read your article on this issue before. Do you have any idea what it might be. The RPM bounces to very low then back to normal.
A. Some of the older Accords would have idle fluctuation because of low coolant, which is what I think I wrote about previously. You could certainly check that, but I am thinking you may have a dirty throttle valve or possibly a bad or maladjusted TPS (throttle position sensor).
Is the Check Engine Light on? You may need to have a good diagnostic technician connect a scanner to read some of the data to determine what is going on. You certainly don’t want to throw parts at it because that can get expensive.
One last thing. Make sure your engine is getting up to the proper operating temperature.
Ÿ Douglas Automotive is at 312 S. Hager Ave., Barrington, (847) 381-0454, and 7218B Virginia Road, Crystal Lake, (815) 356-0440. For information, visit douglasautomotive.com. Send questions to underthehood@dailyherald.com.