Want to learn to drive a stick? Get your own car

Q I have a few years of experience safely driving vehicles with automatic transmissions. However, I would like the opportunity to learn how to drive a manual transmission, even though it may be difficult.

I know of someone who has had experience with stick shifts. The main problem is that I do not know exactly what to say to at least get a civil dialogue going. I am afraid that I may not get the information that I am looking for. Could you please give me some advice on this issue?

A I'm not entirely sure I understand your question. Is it, "How do I find a nice way to ask a friend to teach me how to drive a manual transmission?" Or perhaps a more important question: "How do I ask my friend to allow me to abuse his manual-transmission vehicle as I learn how to shift gears?"

To the first question, just ask this: "If I can come up with a manual-transmission car, will you teach me how to drive it? There's a case of your favorite beverage in it for you."

To the second -- don't ask. If your friend is willing to spend the time teaching you, either rent a car with a manual transmission -- probably a lot more difficult to find than either of us thinks -- or buy an older, inexpensive car with a stick shift and have at it.

Donate it to Courage Center when you're done with it, and if you're sold on shifting gears, buy yourself a fun four-, five- or six-speed car. A new Mazda MX-5 would be fun, don't you think?

Q I have a 2002 Saab 9-5 with a 2.3-liter V4 turbo engine. Since last summer it has shown symptoms of erratic surging by about 200 rpm and pressure fluctuations on the turbo gauge while idling at a stoplight. It happens at 60 miles per hour with cruise control, as well. At high speed, the rpm tends to stay the same, but the turbo-pressure needle swings up and down.

I have changed the fuel pump, spark plugs and fuel filter to eliminate possible fuel-system problems and some but not all vacuum hoses. If I clean the throttle body, the symptoms go away for two or three days and then come back. Could you recommend what I should do to fix this?

A The turbocharger's function on most engines is to increase the amount of air entering the induction system, helping the engine to produce more power. This is also called "forced induction," which perhaps describes the action a bit better.

The turbocharger impeller is driven by hot, expanding exhaust gases coming from the combustion chambers.

The impeller spins a turbine that increases or boosts the pressure of incoming air to greater than atmospheric levels. Instead of the downward movement of the pistons "drawing" or pulling air into the cylinders, the turbo forces air into the cylinders under pressure. The more air forced into the cylinders, the more power the engine can produce.

It's important to remember that turbochargers on most street engines are "demand" systems. As the throttle opens, exhaust volume increases, accelerating the turbo's impeller. The impeller accelerates the turbine, pressurizing the incoming air charge. In short, the turbo makes a little engine think it's a big engine -- on demand.

The key word in your case is demand. At idle, steady cruising speeds and other low-throttle situations, the turbo is basically just idling along, not making any boost. In these situations, the engine is relying on the downward stroke of the pistons to pull the incoming air into the cylinders, creating normal vacuum levels for a normally aspirated (nonturbo) engine.

If you are seeing fluctuations of vacuum in these situations, suspects include the diaphragm in the air-bypass valve that prevents overboost when the throttle is quickly closed, the waste gate that regulates turbo boost, and the electronic waste-gate solenoid regulated by the engine control module (ECM).

I would suggest having the ECM scanned for fault codes from the turbo system. It's also possible, and relatively simple, to use a manual vacuum pump to test the diaphragms on the waste gate, air-bypass valve and vacuum pump.

It might also be worthwhile to check the diaphragm in the fuel-pressure regulator to ensure that it's not allowing raw fuel to be drawn into the cylinders when the engine is developing a vacuum.

Q I have a 2007 Jeep Patriot, and recently two dealerships suggested I get nitrogen instead of air in my tires. It's supposed to deliver better mileage. The cost is about $30 to $40. Is it worth the investment?

A Nitrogen is a better gas for tire inflation because it is completely dry -- no moisture to promote corrosion -- and its pressure fluctuates less over time and as the outside temperature changes.

So, yes, nitrogen in tires is a good thing -- but it's not worth $30 or $40.

Check around, and you'll find dealers and tire shops that offer nitrogen at little or no cost.