Dear Tom and Ray:

I just bought a 1980 Subaru GL5 wagon with a 1600 engine and an odometer showing 257,000 miles. OK, so I'm not the sharpest knife in the drawer. The engine ran rough when I bought it for 600 bucks, but I figured, hey, if Tom and Ray can fix cars, it can't be that tough, right? Well, it's three months later, and I've had a lot of phone consultations with some very nice people who know a lot more about cars than I do. Turns out I have a bad anti-afterburn valve. Of course, the part I need has gone the way of the dodo bird. So, I stuffed a blue plastic Wal-Mart bag under the valve, and the engine smoothed right out. What are the consequences (besides the obvious fire hazard) of making this permanent? -- Tim

TOM: The consequences? Well, for starters, it's going to be hard to bring home all your stuff from Wal-Mart now.

RAY: Actually, there are only two other consequences I can think of. One is that the repair is not going to last, and your problem will return. Think about it. If this was really a viable, long-term fix, we'd all be using Wal-Mart bags to fix our cars. The other problem is that you're going to be breathing burning plastic until the repair does fail. And if you think you're slow on the uptake now, just wait a few weeks!

TOM: The anti-afterburn valve is better known as an anti-backfire valve. It's an early emission-control device that injected pulses of fresh air into the catalytic converter to help burn up any unburned fuel that managed to get that far.

RAY: My brother used the past tense because we suspect the valve's not working anymore. But the nonfunctioning valve is not what's causing your engine to run rough. That's caused by a vacuum leak that has developed BETWEEN the valve and the engine. There's supposed to be an airtight gasket in there. Your gasket has disintegrated.

TOM: Gaskets sometimes disintegrate after 257,000 miles, believe it or not. That now-melted Wal-Mart bag is serving as a temporary gasket. But you can easily make a new one.

RAY: Go to your favorite parts store and buy a piece of gasket material. It's cheap -- a few bucks. Then remove the valve and trace the bottom of it onto the gasket material. Then cut it out, put it all back together, and we guarantee you'll be good for at least another 257, Tim.

TOM: That's 257 seconds, not thousands of miles.