QThis spring I went to replace my air filter, only to discover that mice had chewed out the entire section leading into the throttle body. Did it affect my engine by driving it over the entire winter this way? I checked the filter last summer and it was fine, but in late fall I was still going up to the cabin, which is on a very dusty gravel road. I installed a wire mesh screen on the front side of the new air filter. Is this OK?

AYears ago, I cohosted a TV show on cars that aired on the Speed Channel. We did a segment on changing the air filter and used the producer's older Volvo sedan. With cameras rolling, I released the clamps holding the air cleaner cover and pulled it off, only to discover a three-story mouse condo built with pink fiberglass insulation -- the only thing missing was an elevator. You should have seen the look on the producer's face: It was absolutely priceless!

Rodents and other small critters are the bane of parked automobiles. They nest in air ducts, eat electrical wire insulation and leave "debris" everywhere. I "long-term park" vehicles with dryer sheets strewn about the interior, engine compartment and trunk, and I make sure the windows are open only a fraction of an inch for ventilation. I've even plugged tailpipes and air intakes with rags to prevent invasion.

In your case, a huge hole in the air induction system between the mass airflow (MAF) sensor and throttle body would create a huge drivability issue and light up the "check engine" light -- so I have to assume the opening was between the air filter and MAF sensor. In that case, a significant percentage of incoming air would be correctly metered, but unfiltered. This wouldn't affect drivability much, but would allow airborne dirt and debris into the induction system and engine.

To check for this, pull off the hose on the front of the throttle body and inspect for a film of dirt on the throttle plate or bore. Since any air drawn from the front of the car was still being filtered, only engine compartment air was drawn through the hole.

If there is evidence of dirt, the only thing you can do is clean and flush the throttle body, wiping away as much as possible. Then I'd spray aerosol SeaFoam Deep Creep through a vacuum port into the induction system with the engine running to clean any dirt/debris downstream from the throttle body.

Adding the wire screen, as long as it's not too restrictive to airflow, upstream of the air filter will help prevent large-caliber dirt/debris from reaching the air filter, but with the hole being between the MAF sensor and throttle body, the critters have chewed through the air duct from the outside, not the inside.

QI purchased a 1988 Cavalier knowing that the air conditioner was not working. The refrigerant leaks out overnight, but three garages have failed to find the leak. What should I do?

AHave a shop charge the system with nitrogen and perhaps add a dye to find the leak. At that rate of loss, the leak should be easy to spot. Common areas of leaks are the compressor seals and the condenser.

QI recently purchased a 2007 Chrysler minivan. The van does not have antilock brakes or stability control. Can these features be added to a vehicle that doesn't have them?

ANo. Adding these would be virtually impossible and prohibitively expensive because of the sophistication, complexity and integration of electronically controlled systems on modern vehicles. For example, your vehicle has a simple brake master cylinder. ABS/traction-control-equipped vehicles feature an electronic brake control module, an electro/hydraulic brake control module and individual wheel speed sensors, all integrated with the hydraulic brake system and the powertrain control module.