Question: I bought a used 1979 Eldorado equipped with fuel injection. The problem is that after the engine has idled for two minutes from a cold start, it starts to surge. One second the idle will race up, and the next it will drop to the point where the engine nearly stalls. The car also drives the way it idles, speeding up and slowing down. What is causing this?--M.C.
Answer: Any number of problems could be affecting your Cadillac, but your complaints are common among owners of fuel-injected engines, especially models that date back several years.
Engines with fuel-injection systems are particularly sensitive to gasoline quality. The system works by injecting or squirting a small quantity of gasoline directly into the engine's manifold, rather than allowing gas to be drawn into the air stream in a single carburetor.
The gasoline companies have attributed the problem to engine designs that require absolutely pure gasoline. In turn, the auto makers have accused the gasoline companies of selling dirty fuel, causing the injectors to clog. (Car manufacturers and gasoline companies have improved their products in an effort to eliminate the trouble.)
If you are a motorist, you may be caught in the middle, footing an expensive repair bill and suffering with a car that performs poorly. There are some products that have been introduced to the after-market that may be of some help.
One is a new gasoline filter that can be inserted into the gas tank filler pipe. You simply remove your gas cap and push the filter down into the pipe. After a recommended 7,500 miles, you replace the filter.
The product is being introduced by Filtromatic Corp. of New York, an established manufacturer of filters. Filtromatic officials say the filter mesh will remove dirt but will not interfere with service station gasoline pumps. The estimated cost is under $10.
For details, write to P.O. Box 277, Middle Village, N.Y. 11379.
Q: My car is a 1985 Audi 4000 with 19,600 miles on it. The dealer found heavy carbon deposits on and around the valves and claims this is a result of the gasoline that I have been using. I use Mobil Super Unleaded, and Mobil claims this problem cannot be its fault. Have you run across this problem?--W.S.A.
A: If you have put only 19,600 miles on your car in three years, you are probably puttering around in city driving quite a bit. This sort of usage is terribly hard on an engine and can cause the type of buildup you apparently have.
I am surprised that the service people at the dealership tried to blame the gasoline. The carbon buildups are seldom caused by the type of gasoline you use. Anyway, Mobil is a recognized brand name. In the future, you may want to get your car out on the freeway for a long, high-speed drive periodically, so you can burn off those harmful carbon deposits before they cause major engine problems.
Q: The owner's manual of my 1983 Datsun Maxima suggests I keep 28 pounds of pressure in my tires. I recently had the front end aligned and the mechanics suggested I keep 32 pounds of pressure. Which is advisable?--A.L.B.
A: The recommendation in the owner's manual is based on a compromise between safety, performance, tire wear and riding comfort. Raising the pressure is going to affect all of those items, so if you change the pressure you should do so with caution.
A higher tire pressure may increase tire wear and give a stiffer ride but help the car corner better. Its effect on stopping distance is difficult to estimate. By following the owner's manual instead of relying on a mechanic's opinion, you at least have some assurance that these factors have been considered by engineers.