Question = Car has 58,000 miles.It stalls on very low speed deceleration and restarts immediately..Spark test done and diagnostic scan with no codes expressed. Can the MAF, Crankshaft Positioning,Throttle Positioning sensors,and or the ICM give false negatives when scanned? If not usual then what are possible other suspects. Thanks.
Answer: With no codes in the computer of your Buick LeSabre, it would be hard to diagnose over the computer. The MAF, crank position, ignition control module would not cause the problems you are having. If they were the car would not start right back up. Of the things you listed the throttle or TPS sensor is a possibility. But this will usually set a code in the computer.
If it does not feel like the transmission is jerking, sort of like a stick shift trans where you forget to press the clutch as you are slowing down, then the most common cause is something simple like carbon buildup inside the throttle. Get the throttle body cleaned real well then take an expressway drive and sort of clean it out by doing several very hard accelerations. A dirty throttle will affect your cars idle.
To answer your question about false-negative's when a computer scan, a sensor can have what is called an intermittent problem where the problem occurs so quickly that the computer does not catch it to set a code. This is not very common but I have seen it before. This makes it very hard to repair a car with this sort of condition. The mechanic would have to be driving it and experience it himself while watching live streaming data on his diagnostic computer. Many times he will be able to graph the live data, look at it later and see a glitch. But again this is not very common. Have the throttle cleaned out before you do anything.
In regards to the crankshaft position sensor, when they fail normally the engine will stall and will be very hard to start until it cools down.
And MAF sensor will usually cause poor acceleration or hesitation that acts similar to low fuel pressure. I have had a few that cause stalling but not many.
A bad ignition control module or ICM almost always will cause a car to stall and not restart. Low speed deceleration has no affect on an ignition control module.
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