Letters: Carbon buildup could slow car startup

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Q: I’m a pretty good backyard mechanic but my 1994 Buick LeSabre (124,000 miles) has me stumped. It runs perfectly during the warm temperature months (April-September); however, once the temperature drops below 40 degrees, this car is difficult to start. When starting it on cold days, the engine sputters and coughs. And when I finally do get it started, I have to give it a little gas for a few minutes until it warms up. Then it runs great.

I have replaced the battery, idle air control valve, coolant temperature sensor, fuel filter, spark plugs and ignition wires. I also checked the fuel pressure. With the key on, fuel pressure is 41 psi. What do you think could be wrong? – Ron

A: My first suspicion would be carbon buildup in the intake ports. Carbon deposits in the intake ports can act like sponges, absorbing fuel during cold-starting. This reduces the amount of fuel available for combustion. Cold engines need much more fuel to start and stay running than warm engines. That’s because fuel condenses on colder surfaces so the mixture needs to be richer to start a cold engine. Once the engine warms up, the mixture can be leaned out. If there are carbon deposits in the intake ports, once they become saturated the engine will begin to run better.

Sometimes the only way to clean these carbon deposits is by having the intake system thoroughly cleaned or blasted. You might want to try a fuel tank additive and take the car for an extended drive on the highway. Or, you may want to try a product like Sea Foam. Another possible source of trouble could be the mass air flow sensor. Sometimes they get dirty and can be fixed by cleaning them with a special aerosol. Other times, they need to be replaced.

Q: The heater in my daughter’s 2004 Ford Taurus blows only cold air. I checked the antifreeze and it’s at the proper level. I don’t think it’s a thermostat because the engine does get up to operating temperature fairly quick. I’m wondering if it could be a plugged heater core. I checked the two heater hoses and they both feel hot to the touch. What do you think could be wrong? – George, Chicago

A: A plugged heater core is possible but not likely. When both heater hoses are hot to the touch this generally indicates that there’s sufficient flow of coolant through the heater core. Usually, when the heater core is restricted or plugged, the heater core outlet hose feels much cooler than the heater core inlet hose.

There could be a problem with the temperature blend door or its actuator. The temperature blend door controls the amount of incoming air that is allowed to flow across the heater core. In the full cold position, all incoming air bypasses the heater core. In the full hot position, all incoming air is diverted across the heater core. The temperature blend door, which used to be controlled by a cable on older cars, now, relies on an electric motor to position it accordingly. The temperature blend door in your daughter’s Taurus could be jammed or the electric motor could be faulty.

Questions for Ira Siegel? Call the Auto Advisor Hotline at (708) 633-6839 or e-mail ira.siegel.is@gmail.com. Siegel is an automotive instructor and an automotive service excellence-certified master auto technician.