Texaco Claims Additive Boosts Performance : Gasoline: Treated fuel is said to burn cleaner and improve mileage.

Texaco Inc. on Tuesday laid claim to a long-sought gasoline additive--one that reduces engine deposits in a car’s combustion chamber that can cause rough idling, poor acceleration and power loss.

The company said its new ingredient, to be incorporated in all grades of Texaco gas beginning March 1, also improves mileage and performance while lowering emissions of nitrogen oxides, a smog-forming air pollutant, by an average of 15%.

Since the 1950s, most major oil refiners have relied for much of their marketing punch on detergents and other additives that improve engine performance. Each brand adds its own mix to various octane grades that otherwise are largely interchangeable. Even industry critics agree that most of them do some good.

But the new Texaco additive “can really only be termed a breakthrough,” said David Cole, director of the Office for the Study of Automotive Transportation at the University of Michigan. “I’m not saying that this is a perfect product, but we have seen nothing like it in the marketplace,” said Cole, at a press conference in New York Tuesday.

Internal-combustion motors always have had problems with deposits of unburned fuel that clog engines. But a new, varnish-like deposit began to appear after unleaded gasolines became standard. Companies developed additives that helped to clean carburetors, fuel injectors and intake valves.

“But combustion-chamber deposits are the sort of Holy Grail of the business,” said Christopher Dyson, analyst with the consumer group Public Citizen. “There’s a tremendous value if they’ve been able to solve that problem.”

There also would be great value to the refining industry if the oil companies could meet federal and state standards for cleaner, reformulated gasoline by using such additives, Texaco officials stressed. On Monday they presented test data to the state Air Resources Board, which is requiring that cleaner-burning fuels be available by 1996.

“We have always structured our rules to allow oil companies to devise alternatives to our formula if it reduces the same amount of pollution,” said ARB spokesman Bill Sessa.