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Greetings,

1985 Eldorado, 25K miles
When highway driven at speed (40mph or better) for 15 minutes or more, call will detonate severly upon decelleration. Problem will go away if throttle is flored and kick down into passing gear. The detonation is severe and sounds like a deisel motor. The idle control motor will pulse the throttle to keep engine running. This problem only occurs upon decelleration to a to stop or merge in traffic after driving for at least 10 or 15 minutes at highway speeds. EGR replaced, fuel delivery test done, fuel filter changed, timing checked, car has new exhaust system and new catalytic convertor. Any help appreciated.

Thanks,
OB1-
 

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76 Eldo (54k), 76 Eldo (52k), 78 Eldo (9k), 85 Deville (43k)
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Dieseling on deceleration? That's a new one. Any codes?

You may have a severly leaking injector, a bad MAP sensor, or perhaps a bad TPS. Turn the key on and watch and see if an injector starts dribbling. Also, check to see if your TPS voltage increases smoothly as you depress the pedal. Check the MAP vacuum hose and you may want to just replace the sensor since it's about $15.

Maybe an 02 sensor since it only occurs when hot.
 
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