•Q. Although I like to do my own repairs whenever I can, I don’t know enough about cars to make a reliable diagnosis. Is it ethical for me to use commercial shop mechanics to make the diagnosis and then use that information to do the repair myself? Am I hurting their livelihood by giving them the implied promise of a potential repair job to get a thorough diagnosis, while knowing full well that I will not give them the business?•

TOM: Well, I don’t think it’s ethically confusing. It’s unethical. And not very nice.

RAY: Most shops fold the cost of diagnosis into their posted repair rates. So if you’re paying $75 an hour for repair work, that covers the time spent figuring out what’s wrong with the car.

TOM: Which means that if you simply go in and ask for an estimate (which requires a diagnosis) with little or no intention of having the repair done by that shop, you are taking advantage of them and asking them to work for free. And in my experience, most people don’t like to work for free. Especially when they’re not told that they’re working for free.

RAY: Some people, like my brother, don’t like to work at all, under any circumstances.

TOM: You’re hardly alone in doing this. We have people ask us to look at their car, then make some excuse about not having time or not having the money right now (which is sometimes true). Then they shop the job around to see if someone else will do it cheaper.

RAY: We also have people who call the shop to ask for an estimate on a specific job (so specific that we know they’re reading it off of someone else’s estimate). And since they’ve asked us for a price, we have to call to get parts prices and figure out how much labor will be involved, which is time-consuming.

TOM: So this kind of thing is done. But that doesn’t make it nice. The ethical thing to do is to be honest with the shop, and then pay them for their time.

RAY: If you know that something is wrong with your brakes but you don’t know exactly what, let the shop know that you’re hoping to do the repair yourself, but you’d like to pay them to do the diagnosis.

TOM: Then pay them their regular rate for the time and expertise they put into figuring it out for you.

RAY: Similarly, if you’re looking to check up on another shop’s estimate, be honest. That’s what we’d prefer. Say that you just got a diagnosis and an estimate from another shop, and you were hoping to find out if it seems like it’s in the right ballpark.

TOM: That’s a lot easier for us to answer than it is for us to go chasing parts prices for half an hour. And we’d do that for most people, figuring that if we’re helpful, perhaps we’d get their business another time.

RAY: Some shops may tell you that they don’t have time to help you. But that’s probably because they, what? Don’t have time to help you. So then you call another shop. But by giving each party in a transaction the opportunity to know what’s really going on, you’ll be on solid ethical ground.

•Q. I have a ’93 Toyota pickup with a six-cylinder engine. I live at 6,000 feet, and when I’m there, my truck runs fine. But when I go down to sea level, the truck is very hard to start. It cranks but has a hard time turning over, then when it does finally turn, it runs roughly until I get the truck on the road and the RPMs are up. Then it runs fine. Right now I’m staying at a friend’s house that is at about 1,000 feet elevation. I can start the truck fine up here, but as soon as I go down to sea level, it becomes very hard to start, whether the engine is hot or cold. The elevation is the only variable. Any ideas?•

TOM: Well, first you have to tell us how long the “Check Engine” light has been on. Then we’ll decide how many yards to penalize you for “withholding information.”

RAY: Problems like this rarely occur without the computer setting a Check Engine code. So if your light IS on, you need to have the vehicle scanned for trouble codes. That’ll usually help pinpoint the source of the problem.

TOM: If the Check Engine light isn’t on yet, perhaps because you spend limited time at sea level, where the problem occurs, then you may have what’s called a “pending code.” That means the computer has detected a problem but it hasn’t happened with enough regularity to set the Check Engine light yet.

RAY: But a scan still will tell you if there’s a pending code stored. So next time you’re at sea level, while you’re experiencing this problem, take the truck to someone and have it scanned.

TOM: My first guess would be that you have something like a faulty air-flow meter. But we don’t have to guess. Your car’s engine management computer knows what’s wrong. Ask it.

Got a question about cars? Write to Click and Clack in care of this newspaper, or email them by visiting the Car Talk website at www.cartalk.com.