Western-Star

Wheels: An e-mail from Gary of Dayton says, "I saw E-85 for sale at a gas station for $2.75 which is $0.45/gallon less than what 87 octane sells for. What gives? I thought E-85 would be higher than standard 87 octane gas."

Halderman: Many people are confused about E-85 which is becoming more available in the area. E-85 is 85 percent ethanol (also called ethyl or grain alcohol) and 15 percent gasoline. The resulting combination of alcohol and gasoline creates a fuel with a high anti-knock index with a pump octane of about 100. However, the heat energy is about 25 percent less. This reduced heat production reduces fuel economy about 20 percent to 30 percent.

For example, a Chevrolet Silverado pickup truck equipped with a 5.3 liter V-8 engine is rated by the EPA with a fuel economy of 15 mpg city and 20 mpg highway. If E-85 is used, the fuel economy will drop to 11 mpg city and 15 mpg highway. Therefore, even with a cost reduction, the cost of using E-85 is greater than using gasoline. However, if E-85 is used, at least the ethanol in the E-85 is a renewable resource. E-85 should only be used in vehicles designed to use it and are usually labeled as being flex-fuel vehicles.

Wheels: Bob writes by e-mail, "I have a 1995 Olds Cutlass Supreme SL with a 3.4 DOHC V-6 engine, and with 121,000 miles. After the car has sat in the garage overnight, the next morning when I go to start the engine the idle speed races, surges and chuggles, from 4000 RPM to a few hundred RPM. After a couple of minutes, the engine heats up, the RPM becomes steady; and for the rest of the day of stop and go driving it runs just fine.

My friends say it is a vacuum leak but I can't find any problem. In 2002, with 84,000 miles, I had the intake manifold gasket replaced for basically the same reason of RPM surges when the car sits in the garage overnight and is cold the next morning. My service manual says, among other things, it could be the heated oxygen sensor (HO2S), or vacuum leaks, or air leaks. The spark plugs and wires are new. I need your advice. Thanks."

Halderman: While the intake gasket could have failed again, other possible causes include a defective engine coolant temperature (ECT) sensor. When the engine is cold, the resistance of the sensor is high and becomes lower as the engine warms. If there is a poor electrical connection on the sensor, the engine computer would then assume that the engine is colder than it actually is and command a higher idle speed. I suggest that you have it tested by a professional technician who should look at the idle air control (IAC) valve commanded position to determine whether or not the high idle is being commanded or is a result of an air (vacuum) leak. Normal IAC counts or percentages should be 15 to 25. If being commanded high (higher IAC counts), then the ECT sensor is the most likely reason. If the IAC is not being commanded high, then this would tell me that there is a vacuum leak.

E-mail James Halderman at jhalderman2@juno.com., or write him in care of: Wheels, Marketing Publications Department, Dayton Daily News, 1611 S. Main St., Dayton OH 45409.