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Discussion Starter #1
Stepson bought a 1985 Marquis recently(2days sgi). It stalls out at lights and runs rough. The engine seems to be good, starts ok, but I’m not familiar with this car at all. Some of the forums have mentioned cleaning air sensors. The exhaust blows white when started and smells of unburnt fuel all the time. Is there an idle adjustment screw? I’ve cleaned the air sensors on the housing for the air filter, made sure all hoses were attached properly too. The former owner said it was “mechanically sound“ and the boy made the deal before I could really look it over. I’m afraid the slimy seller did something to make it run well just long enough to sell it. Any help would be greatly appreciated.
 

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Sounds like it's running rich, here's the most likely causes:
  • Vacuum leaks. As excess oxygen enters the engine the ego's indicate more on the lean side to the PCM causing it to richen the mixture.
  • Bad MAP sensor indicating incorrect load.
  • Lazy EGO sensors incorrectly indicating lean to the PCM.
With the age, if the vacuum hoses look old replace them all and start from there.
 

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Discussion Starter #3
Ok thanks, gives me something to start with. I have a buddy that works on these older cars. He came by and basically said because it sat for a few years in a garage we should have just changed fluids and tightened gaskets, plug wires, plugs, and fuel filters. The guy we bought it from said he had done that but I doubt it now.
 

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The unburnt fuel could be an injector fault . I would pull the plugs and examine for any clues , replace as needed. .You may need to carry out a compression test also if nothing obvious . Make sure there is no drop in coolant level which could be indicative of head/ gasket fault .
 
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