Possible causes of unintended acceleration

Dear Tom and Ray: Do you know of any sudden-acceleration problems with Subaru vehicles? My 2004 Outback suddenly accelerated, on its own, while my foot was on the brake. I had to stand on the brake to avoid surging ahead into traffic. It continued at super-high revs when placed in Park, then subsided on its own. The same thing just happened to my husband, under the same conditions. Subaru claims ignorance, even though I found several similar complaints online. I am taking it to the dealership tomorrow, but wondered if you have any clues as to what could have caused the problem.

Jaye

Ray: In our experience, unintended acceleration has a number of causes. The simplest one is someone accidentally stepping on the gas pedal when intending to step on the brake. Or stepping on both pedals at the same time -- and the gas pedal wins.

Tom: Obviously, if you put it in Park and take your feet off the pedals, and the engine is still revving high, that's not your problem. But misapplication of the pedals is a real problem -- more so in the winter, when people wear big, honking, clodhopper boots that are wide and that make their feet numb to what they're stepping on.

Ray: We've also seen accelerator pedals get stuck under floor mats. So don't overlook the simple stuff.

Ray: And then there are the more mysterious causes of "UA." These are the cases in which the computer is suspected. The fact is, every car built these days has computerized engine controls. One of those controls allows the computer to open the car's airway beyond the throttle.

Tom: You should report your problem to NHTSA -- the National Highway Traffic Safety Administration. It maintains a database of safety complaints. And if it sees a pattern of problems, it has the ability to launch an investigation that could lead to a recall. It's at www.nhtsa.gov, or by phone at (888) 327-4236.

Ray: Obviously, NHTSA hasn't had a sufficient number of complaints about Subarus to make it think there's a defect. But it does a pretty good job of watching this stuff. So it's worth adding your complaint to the database when you have a problem that directly affects your safety -- and this certainly fits the bill. Good luck, Jaye.

Tom: This allows the computer to adjust the idle speed when, for instance, the air conditioner comes on and draws power from the engine.

Ray: But since it can adjust the idle speed on its own, it -- theoretically -- has the ability to malfunction and cause unintended acceleration. Unfortunately, it's notoriously hard to diagnose unless your mechanic can actually catch it in the act.

Tom: And as we said, this can happen on any modern car, not just Subarus.

Ray: So, if you're absolutely sure that your foot or your floor mat was not the culprit, ask your dealer to keep the car for a few days and get the service manager to drive it home. With a little luck, the problem will happen to him, and he'll be newly motivated to fix it.