Like most modern cars, everything under the hood of my Subaru is controlled by a computer. But when something goes wrong with mine, rebooting the computer only makes matters worse at least for a while.
When something gets out of whack in the engine compartment, the computer "throws a code" and the check engine light comes on. I take it to my mechanic, who attaches a gizmo to the computer, downloads the error code and hopefully fixes the car. Before I get it back, however, he resets the computer to clear the code. But that creates another problem.
The first error code occured in June. The car started, but ran roughly and the check engine light came on. I was in Newport Rhode Island on a Sunday morning. It was 7 am. Somehow I managed to coax the thing home, where my mechanic diagnosed the problem as a misfire. He replaced the spark plugs and ignition coil, reset the computer and the car began stalling as soon as I got off the parking lot. It stalled in the roundabout, at a stop sign and as I coasted back into the shop. But when the mechanic started it, it ran just fine.
No surprise there.
A few days later the light came on again. This time the code indicated a catalytic converter malfunction. The mechanic did the work, reset the code, I left, and the car immediately started stalling. After about 20 minutes the problem went away.
This went on a few more times until my local dealer finally explained what was happening.
When the computer is reset on a 2005 or later, manual transmission Subaru automobile, certain configuration settings are erased including the air/fuel mixture ratio for the car. No one knows exactly why this happens. But when it does, the vehicle runs roughly until the computer "relearns" the proper settings from the air flow sensors a process that can take a few minutes or a few hours.
Unfortunately for me, I have a 2005 Subaru Forester with a manual transmission. According to the dealer this is a known problem that persists through the 2009 model year. They just forgot to tell me about it.
The $810 bill for the catalytic converter was covered by warranty, but the new plug wires and coil a $550 repair wasn't. But it's a good thing I replaced them, the dealer says.
"Misfiring can lead to premature catalyst failure." Then the computer would throw an error code. The mechanic would have to reset the computer. And I'd be back where I started.