Trying to Stay Cool About Idle Problem

Question: I purchased a 1984 six-cylinder Oldsmobile Omega in November, 1984. When using the air conditioning, there is excessive vibration of the steering wheel during idle. The dealer replaced the air conditioning compressor and the evaporator. The problem still exists. What could be the cause?--D.E.

Answer: It’s not clear what you mean by “excessive” vibration, because most cars will vibrate somewhat when an air-conditioning load is placed on the engine. I am surprised that the dealer would have replaced the evaporator to solve a vibration problem, because that is very unlikely to cause such a condition.

An air-conditioning compressor puts a sizable load on the engine, and when the car is stopped, that load can cause vibrations in the car frame. That’s especially the case in smaller engines and on engines that don’t idle properly to begin with.

The Omega has an automatic control that speeds up the engine idle by 75 revolutions per minute when the air-conditioning compressor is on. If the system is working and the car is properly tuned, the vibration should be minimized. You may also suggest that the mechanics make sure the motor mounts are secure.

Q: I know this sounds crazy, but squealing brakes can be cured 90% of the time by spraying the brake pads with LPS or WD 40. It works.--M.S.

A: Your idea not only sounds crazy, it’s a dangerous mistake. Those two substances are lubricants, and by spraying the pads, you are significantly reducing the braking power of your car.

Brake squeal is an annoyance that is usually caused by glazing of the brake pads. This often affects very hard brake pads, such as ones with a high metallic content. Sometimes you can eliminate the squeal by switching brake-pad brands.

Also, a lubricant or insulation material can be applied to the metal backing plate of the brake pad, which will dampen the high-frequency vibrations that cause the squeal. In either case, you should never lubricate the pad itself.

Q: This regards my 1985 Thunderbird with fuel injection. My problem is that regardless of the engine being hot or cold, the motor stumbles or hesitates when stopping at a traffic light. Of course, when the accelerator pedal is pushed hard, the motor jumps. Dealership mechanics claim everything is normal, but is it?--E.C.G.

A: The fuel-injection system on Fords is not always as quickly reacting as a carburetion system, so your problem may be “normal” though undesirable. The lag time is most pronounced on a light acceleration, and some drivers never notice the hesitation.

Fuel injection is a system in which small amounts of gasoline are pumped directly into the air stream entering an engine’s combustion chamber. In a carburetion system, a stream of fast-moving air draws gasoline up small passageways, much like the action of a sprayer bottle.

Both carburetion and fuel injection are controlled by various vacuum and electronic equipment that take readings of engine temperature, outside temperature, the chemical composition of exhaust gas and the load on the engine.

A hesitation, especially during a mild acceleration when such problems seem to expose themselves most often, could be induced by any number of these factors, including the exhaust-gas recirculation system.

The hesitation should certainly be no more than a split second. If it lasts a full second or longer, you should have the car looked at again. A delay longer than just the bat of an eyelash would be difficult to take into account in every driving situation.

Ralph Vartabedian cannot answer mail personally but will respond in this column to automotive questions of general interest. Do not telephone. Write to Your Wheels, You section, The Times, Times Mirror Square, Los Angeles 90053.