Hello. 1991 740 auto sedan with 157,000 miles. Just got this car about 3x weeks ago. Have just been using locally thus far around town. Horrible gas mileage I think. Only 16mpg ! Have replaced sparkplugs, IAC valve, engine temp sensor, air filter. Cleaned oil/flametrap(it was clean). Checked for any manifold, hose, line leaks. None. No bad codes being displayed. So as I am frustrated with poor local gas mileage and can not think of any thing further to check I am thinking of replacing the oxygen sensor. Do you think that would help my local gas mileage or would it mainly help my highway mileage ? By the way my oxygen sensor goes onto catalytic converter not down pipe or exhaust manifold - is that correct /normal ?? My 240 goes to exhaust manifold. Is NGK 25002 only sensor I can use ??? It is kinda pricey. Thanks in advance for your thoughts/ replies / input.
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' 91 740 sedan nearly 157,000 and ' 87 240DL auto nearly 135,000
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